Russian diplomats and their families are preparing to leave the UK after being expelled over the Salisbury spy attack.
Removal vans and diplomatic cars have been leaving the embassy in London.
The UK expelled 23 diplomats after Prime Minister Theresa May said Russia was "culpable" for the poisoning of Sergei Skripal and his daughter.
Later on Tuesday, the government will decide whether to impose further sanctions on Russia.
Mrs May is chairing a meeting of the National Security Council.
Moscow has denied all involvement, and is expelling 23 British diplomats in response.
The UK diplomats have until Saturday to leave Russia.
The Kremlin is also closing down both the British Council in Russia, which promotes cultural ties between the nations, and the consulate in St Petersburg.
The Russian Embassy said around 80 people - including the Russian diplomats and their families - will leave London today, which is the deadline given by Mrs May.
A small crowd gathered outside the embassy and waved goodbye to people carrying suitcases, children and pets as they boarded vehicles.
The BBC`s diplomatic correspondent James Robbins said launching a second round of measures "risks an endless tit for tat with the Kremlin".
But "not to do so risks accusations of weakness from some quarters," he added.
Russian former military intelligence officer Sergei Skripal, 66, and his daughter Yulia, 33, remain critically ill in hospital after being found slumped on a bench and unconscious on 4 March.
They had been exposed to a nerve agent of a type developed by Russia called Novichok, the UK government claims.
More than two weeks on from the attack, the head of counter-terrorism policing in the UK, Met Police Assistant Commissioner Neil Basu, said the focus of the Salisbury investigation is "on the movements of the Skripals".
Officers are trawling through 4,000 hours of CCTV footage and have already taken 400 statements with more to come.
"It is going to take weeks, possibly months," Mr Basu told BBC Radio 4`s Today programme, adding: "This is going to be frustrating for people.
" Meanwhile, following a phone call between Japanese Prime Minister Shinzo Abe and Mrs May, Downing Street said Japan condemned the Salisbury attack and "shared our outrage".
The leaders of France, Germany and the US have already pledged support for the UK in a joint statement and the EU offered its "unqualified solidarity".
EU leaders will meet at a summit in Brussels on Thursday to discuss any potential response to Russia.
Labour leader Jeremy Corbyn said the UK must still deal with Russia despite "all fingers" pointing to it over the Salisbury spy attack.
He said he would "do business" with Russian President Vladimir Putin but assertively and on the basis of the UK`s values.
Foreign Secretary Boris Johnson previously said it is "overwhelmingly likely" that President Putin ordered the nerve agent attack.
Russia said the accusations were "shocking and unforgivable".
Mr Skripal, a retired military intelligence colonel, came to the UK in 2010 after being released from prison in Russia.
He had been jailed in Moscow in 2006 for spying for Britain and passing the identities of Russian secret agents in Europe to MI6, the UK`s Secret Intelligence Service.
His daughter, Yulia, flew into the UK from Russia on 3 March, the day before she and Mr Skripal were found on a bench near The Maltings shopping centre in Salisbury, Wiltshire.

With the world’s second-biggest proven reserves of oil, Saudi Arabia seems an unlikely aspirant to the nuclear-energy club.
Yet the largest oil exporter plans to build at least 16 nuclear reactors over the next 25 years at a cost of more than $80 billion.
The Saudis see atomic energy as a way to ease their dependence on finite fossil fuels.
But they are also driven by competition with their rival Iran, which has multiple nuclear facilities.
Whatever the motivation, the turn to nuclear power by Saudi Arabia, and several other countries in Middle East, raises the risk of a nuclear arms race in the most unstable part of the world.
What’s the security risk? Most nuclear reactors are fueled with enriched uranium, which means countries that want nuclear power must either import the stuff or have their own enrichment capability.
Saudi Arabia is insisting on the latter, which could be worrisome, given that highly enriched uranium can be used to build nuclear weapons.
Another type of reactor is powered by raw uranium, which Saudi Arabia possesses, but that type produces plutonium, another fuel for nuclear arms.
Why does Saudi Arabia want nuclear power now? Much of the government’s plan for the future, called Vision 2030, is based on diversifying the Saudi economy to prepare for the day when oil and natural gas wells run dry.
At the same time, electricity demand in the country has risen by as much as 9 percent a year since 2000, compared with less than 1 percent in developed countries such as the U.
, according to Bloomberg New Energy Finance.
Water desalination is a large draw on power in Saudi Arabia.
Why nuclear power instead of just renewables? Solar energy would seem like a good option for Saudi Arabia, and the kingdom has plans to develop 9.
5 gigawatts of solar and other renewables by 2023.
The abundance of sunshine there would make solar much cheaper than nuclear power.
Under recent contracts awarded in the region, electricity from solar power costs about $30 per megawatt hour, less than half the costs of nuclear power, according to Bloomberg New Energy Finance.
On the other hand, solar power requires either battery installations, to store energy, or alternative power sources, for when the sun isn’t shining.
And solar doesn’t have the prestige of nuclear power, which demonstrates a certain level of scientific achievement.
Does Saudi Arabia want nuclear weapons? In an interview with the U.
television network CBS aired in mid-March, Mohammed bin Salman, the Saudi crown prince who effectively runs the country for his father King Salman, said, “Saudi Arabia doesn’t want to own a nuclear bomb.
But without a doubt, if Iran develops a nuclear bomb, we will follow suit as soon as possible.
Is Iran developing a nuclear bomb? Though Iran has consistently denied any interest in pursuing atomic weapons, its uranium-enrichment practices contributed to deep mistrust in the past.
In a 2015 deal with world powers -- including the U.
under President Donald Trump’s predecessor -- Iran agreed, in exchange for the lifting of international sanctions, to decommission its plutonium-producing reactor and to limit its refining of uranium to no more than the level needed to fuel power plants.
The Saudis have embraced Trump’s efforts to upend that agreement.
The president argues that the Iranians can’t be trusted to abide by the deal and that, in any case, they will be free to pursue nuclear weapons when it expires after 15 years.
What’s the problem between Iran and Saudi Arabia? The two are vying for dominance in the Middle East.
Their forces and proxies are arrayed against each other in the civil wars in Syria and Yemen.
Each purports to lead the Islamic world, Saudi Arabia because of its role as the custodian of the holy places Mecca and Medina, Iran because of its Islamic revolution of 1979.
The majority of Saudis follow the dominant Sunni branch of Islam, while most Iranians are Shiites.
The rivalry has intensified with the rise of Prince Mohammed, who is particularly hawkish when it comes to Iran.
What happens next? The Trump administration, eager to revive the torpid American nuclear industry, is pushing Saudi Arabia to consider U.
companies -- such as Westinghouse Electric Co.
and Exelon Corp.
-- for its nuclear contracts instead of competitors from Russia, China and other countries.
 But the U.
is reluctant to offer the Saudis deals without a prohibition on any uranium enrichment or fuel reprocessing in-country.
The United Arab Emirates, a Saudi ally, agreed to that so-called "gold standard" a decade ago to facilitate the inclusion of some U.
parts in its four Korean-built reactors, the first of which is expected to go online this year.
What do the Saudis say? They note that, unlike the U.
, Saudi Arabia has large uranium deposits and wants to be self-sufficient in the preparation of nuclear fuel.
Saudis point out that Iran is permitted under the 2015 accord to enrich uranium for peaceful purposes and say they want the same right.
Who else in the region is going nuclear? The U.
is set to become the first Arab nation with utility-scale nuclear power when it starts operating its plants, estimated to cost $25 billion.
While the U.
is a major oil producer, it relies on imported gas to generate much of its electricity.
Egypt, the most populous Arab nation, has signed a $30 billion deal with Russia’s Rosatom to build four nuclear plants.
And Jordan, which has negligible energy resources, has signed construction deals with Rosatom and U.
-based X-Energy in a program that could cost as much as $12 billion, according to Bloomberg New Energy Finance.
While no Arab nation is known to have a nuclear arsenal, Israel, which began operating a plutonium-production reactor in 1963, possesses enough material for between 100 and 170 atomic weapons, according to an estimate by the Washington-based Carnegie Endowment for International Peace.
Israel has never acknowledged having nuclear arms.
The Reference Shelf.

A sixteen-year-old boy has rejected an appointed role as the deputy commissioner of a regional state in Somalia because of security fears.
Faysal Abdullahi Omar was to take up the role in Jowhar, the headquarters of the south-eastern state of Hirshabelle.
The high school student told the BBC that he feared the role would make him a target of Islamist militant group al-Shabab.
The militant group operates in the region.
Omar says he was not consulted about the appointment, which are made by Somali clan leaders, and he wants to instead focus on his studies.
"Now I am studying in my high school and I am going to finish in few months, I want to go to university and build my future", Omar told the BBC`s Somali Service.
He said he has avoided school for days after receiving the offer letter.
Omar`s parents also had reservations about the appointment.
But others in the community told him that it would be an opportunity to be a "role model to the youngsters", he said.
"I met a lot of people who are pushing me to take this job," he said.
Jowhar lies north of the capital, Mogadishu, and is under the control of the Somali government.
Al-Shabab control the surrounding localities.
A few weeks back, an MP and a regional minister were killed in the region by the militants.

Web surfers know their online data is a gold mine, but what’s it really worth? They may soon find out.
The European Union is introducing tougher rules for how data collectors gather and use its citizens’ information, and lets consumers control their own data.
Starting May 25, all 28 EU nations will be applying the General Data Protection Regulation, which sets new standards for any holder of sensitive data, from Amazon to your local government council.
These rules will apply to any company that collects the personal data of EU residents.
Plenty of firms are scrambling to make sure they’ll be able to comply.
What will the GDPR do? Companies will have to post clear notices for users and get their “unambiguous” consent to collect data, instead of burying an OK inside fine print and legal jargon.
That means the EU will no longer tolerate the confusing “terms and conditions” that must be agreed to while signing up for a fitness tracking app or ordering groceries online.
It will be as easy for consumers to opt out of giving consent as to opt in, and they’ll have the right to refuse that their data be used for direct marketing purposes.
Consumers will have the right to retrieve their data and give (or sell) it to another business.
Collection of data on children under the age of 16 will be banned without parental approval.
What types of data are we talking about? Anything the EU has determined to be “personal data.
” If the data is sensitive in nature and can be linked to a person, it falls under this umbrella of protection.
This includes credit card numbers, travel records, religious affiliations, web search results, biometric data from wearable fitness monitors, and internet (IP) and personal computer addresses.
It doesn’t include news articles, legal actions or public records.
Who must follow these rules? Any entity “processing” personal data by collecting it, storing it or disseminating it.
This means it’s not just social networking sites, search engines and big online retailers.
The rules also apply to information collected by schools, chat rooms, property management companies and even Scoutgroups.
What’s this going to cost firms? A survey of Fortune 500 firms shows they are, on average, setting aside $1 million for the added technology costs.
Just over a third of those polled are budgeting $501,000 to $1 million for new permanent staff.
Firms listed in the FTSE 350 see technology putting them out 430,000 pounds ($600,000) and staffing another 201,000 to 400,000 pounds.
What will they need to do to comply? Firms and organizations with more than 250 employees will have to hire a data protection officer, who will be responsible for making sure the rules are followed through employee training and compliance audits.
If a firm is smaller than 250 but is collecting large quantities of sensitive data, it will also need a DPO.
If there’s a data breach, electronic data collectors will have to notify authorities within 72 hours and will have to alert customers in a timely manner if the breach poses a risk to them.
So situations like Uber’s attempts to cover up of its 2016 data hack, or the slow release of information on Yahoo’s massive breach in 2013 will now be punishable with huge fines.
What’s the penalty for non-compliance? Fines of up to $12.
4 million (10 million euros), or 2 percent of annual worldwide revenue, whichever is higher.
In cases of negligence or violating the conditions of consent and infringing on data subject rights, the fines can go as high as $24.
8 million, or 4 percent of annual worldwide revenue, whichever is higher.
If Google violated the rules, for example, fines could be more than $4 billion since its parent company, Alphabet, had more than $110 billion in revenue in 2017.
In worst-case scenarios, the people responsible could face prison sentences.
But it’s likely that any legal action taken against deep-pocketed web service companies would be fought in the courts for years.
How will life change for consumers? They’ll have free access to the data that’s been collected on them and more information on how it’s being used.
Data will be destroyed when it is no longer needed for the original task.
To request access to their data, consumers will contact the data controller or controllers, whose contact info must be provided to consumers whenever information is collected.
And because consumers will own their data, eventually they may be able to trade things like gift certificates from Zara in exchange for their shopping histories with J.
What data can consumers get removed? Through the “right to be forgotten,” citizens can force organizations to erase information that was illegally gained, or no longer holds true.
Data that serves no current purpose, or has been used for direct marketing, could also be on the chopping block.
In some cases, consumers who don’t give permission for websites to use their information may not be allowed to post on social media or consumer review sites.
What happens to sites already collecting personal data? They’ll need to make sure that the data they’ve collected adheres to new protocols.
If they didn’t originally ask permission in a clear way to collect the information, or they didn’t let the subject choose whether to share it, they’ll need to ask again.
The risk is that consumers will withdraw their consent, wiping out databases full of information.
One company that could take a hit is Facebook, which hoped to combat slower growth in European users with added revenue from more tailored ads.
But it’s not all bad news.
“This is a chance for a lot of sectors to let customers know they are doing a good job protecting data,” said Bloomberg Intelligence analyst Tamlin Bason.
He also pointed to potential winners: the large cloud companies that have the resources to become compliant before GDPR goes live.
“That will help sell their data protective services.
” The Reference Shelf — With assistance by Jeremy Kahn.

Former French President Nicolas Sarkozy was detained for questioning by police in an investigation into suspected illegal financing of his successful 2007 campaign, a person familiar with the matter said.
A special financial crimes unit questioned Sarkozy Tuesday morning in Nanterre, near Paris, the first time the former head of state has spoken to investigators in a probe that began in 2013.
The police can hold him for 48 hours before deciding whether to press charges or release him.
The detention was first reported by newspaper Le Monde.
Sarkozy retired from politics -- for the second time -- in late 2016 after placing a distant third in the primary to be the candidate of the center-right Republicans.
He’s remained active behind the scenes as his party looks to rebuild after failing to make the second round of the 2017 presidential elections.
He also speaks occasionally to President Emmanuel Macron, according to French press reports.
Parisian investigative judges began tapping Sarkozy’s phone in 2013 as part of an investigation into whether he received funds from Muammar Qaddafi’s former regime in Libya ahead of the May 2007 election.
Sarkozy first retired from politics after failing to win re-election in 2012.
Calls to Sarkozy’s office and to his spokeswoman weren’t immediately returned.
Prime Minister Edouard Philippe, asked on RMC Radio about Le Monde’s report, said he would have no comment on the legal process.
Sarkozy 2012’s campaign is also under investigation for allegedly falsifying receipts to get around spending limits.
— With assistance by Gaspard Sebag.

Former French President Nicolas Sarkozy was detained for questioning by police in an investigation into suspected illegal financing of his successful 2007 campaign, a person familiar with the matter said.
A special financial crimes unit questioned Sarkozy Tuesday morning in Nanterre, near Paris, the first time the former head of state has spoken to investigators in a probe that began in 2013.
The police can hold him for 48 hours before deciding whether to press charges or release him.
The detention was first reported by newspaper Le Monde.
Sarkozy retired from politics -- for the second time -- in late 2016 after placing a distant third in the primary to be the candidate of the center-right Republicans.
He’s remained active behind the scenes as his party looks to rebuild after failing to make the second round of the 2017 presidential elections.
He also speaks occasionally to President Emmanuel Macron, according to French press reports.
Parisian investigative judges began tapping Sarkozy’s phone in 2013 as part of an investigation into whether he received funds from Muammar Qaddafi’s former regime in Libya ahead of the May 2007 election.
Sarkozy first retired from politics after failing to win re-election in 2012.
Calls to Sarkozy’s office and to his spokeswoman weren’t immediately returned.
Prime Minister Edouard Philippe, asked on RMC Radio about Le Monde’s report, said he would have no comment on the legal process.
Sarkozy 2012’s campaign is also under investigation for allegedly falsifying receipts to get around spending limits.
— With assistance by Gaspard Sebag.

Vladimir Putin isn’t concerned that U.
President Donald Trump hasn’t called to congratulate him on his record victory in Russia’s presidential elections, the Kremlin said.
“We should not consider this an unfriendly step” and Putin remains open to normalization of relations with the U.
where it’s in Russian interests, Kremlin spokesman Dmitry Peskov told reporters on a conference call Tuesday.
“There’s no need to exaggerate anything.
” Hinting that there’s still time for a telegram or call from the White House, Peskov added: “Tomorrow’s another day.
” Many foreign leaders have already congratulated Putin since he won 77 percent of the vote in Sunday’s election, while others couldn’t call because they were too busy “or for other reasons,” he said.
The White House said Monday that Putin’s re-election to a fourth term was unsurprising and that there were no plans for Trump to make a congratulatory call.
There’s been a mixed response from other world leaders.
criticized the conduct of the election amid rising tensions after it blamed a nerve-agent attack on Russia, which denies involvement.
While German Chancellor Angela Merkel did offer congratulations, French President Emmanuel Macron pointedly wished success “to Russia and the Russian people” in a phone call with Putin, according to a statement from the Elysee Palace.
Putin received congratulations from Chinese President Xi Jinping, Turkish leader Recep Tayyip Erdogan, Indian Prime Minister Narendra Modi, Japanese Premier Shinzo Abe and the leaders of most former Soviet republics, according to the Kremlin’s website.