Russian Federation warned it would retaliate against the U.K. Russia's foreign ministry said it's also closing the British Consulate General in St. Petersburg and the British Council in Russian Federation.
Russia's Ambassador to the United Nations, Vassily Nebenzia, repeated Moscow's denial that it had anything to do with the poisoning and called for proof of its involvement.
UK Prime Minister Theresa May gave the 23 Russian diplomats - whom she described as undeclared intelligence officers - a week to leave on Wednesday as she accused the Russian state of being "culpable" for the attack in Salisbury. They are now in critical condition in a local hospital.
"Any reference or mention of our president in this connection is nothing but a shocking and unforgivable violation of the diplomatic rules of propriety". He said Russia's recent provocations need a tough response, including action against Russian oligarchs with questionable ties who have used London as a safe haven. The attack on Skripal and his daughter has brought relations between Russian Federation and the U.K.to their lowest since the end of the Cold War.
On Friday, police said they were treating the March 12 death of exiled businessman Nikolai Glushkov as murder after a post-mortem found he died from 'compression to the neck.
"We can be reassured by the strong support we have received from our friends and allies around the world", May said at the Conservative Party's spring forum in London.
It said this was a response to Britain's "provocative actions" and "baseless accusations over the Salisbury incident".
On March 15 Britain, France, Germany and the United States say in a rare joint declaration that "there is no plausible alternative explanation" to Russian involvement and call on Moscow to provide "full and complete disclosure" of the Soviet-era chemical programme that developed Novichok.
The UK government says they were poisoned with a nerve agent of a type developed by Russian Federation called Novichok, and PM Theresa May said she believed Moscow was "culpable".
When the Brits and others point to the Kremlin over this extraordinary case, it is seen as yet more proof Russian Federation is under attack.
Moscow has now also opened their own investigation into the attack on Yulia, who is a Russian citizen.
On March 13 Russian Foreign Minister Sergei Lavrov says that Moscow is "not guilty" of the poisoning and is ready to cooperate with London.
The Russian expulsions come after Britain issued a travel warning to people in or planning to travel to Russia.
Speaking to the AP, he called it unlikely that some of the nerve agent could have gone missing in the years after the 1991 collapse of the Soviet Union.
Mr Putin's spokesman Dmitry Peskov said the final decision on retaliatory measures "will, of course, be made by the Russian president", adding: "There is no doubt that he will choose the variant that best of all corresponds to the interests of the Russian Federation".
The military-grade nerve toxin that poisoned former Russian agent Sergei Skripal was planted in his daughter's suitcase before she left Moscow, The Telegraph newspaper reported, citing unidentified sources.
Labour leader Jeremy Corbyn, whose response to the attack has led to criticism from some on his backbenches, said "the evidence points towards Russia" being responsible - but the possibility of gangsters being behind the attack rather than the Kremlin could not be excluded.