Britain says blame for the poisoning of Sergei Skripal and his daughter in the English city of Salisbury lies with the Russian state.
In addition to the expulsions, the UK has announced measures that include increased checks on private flights, customs and freight as well as a boycott of this year's Fifa World Cup in Russia by ministers and the Royal Family.
They are, reportedly, as much as ten times more lethal than other nerve agents, such as sarin, one of the chemical weapons that Saddam Hussein used against the Kurdish population during the Anfal campaign, or VX, which North Korea used in Malaysia last year to murder the president's estranged half-brother.
In their statement, Trump, Macron, Merkel and May cited "a pattern of earlier irresponsible Russian behavior" and called on Russia to disclose details of its Novichok program to the Organization for the Prohibition of Chemical Weapons.
However British Foreign Secretary Boris Johnson told the BBC that Britain is "entirely in conformity" with OPCW procedures and is sending a sample of the nerve agent to the watchdog for examination.
Ambassador Alexander Yakovenko also told Russian TV that the embassy had received threats against its diplomats and said it was working with UK police, Russia's Tass news agency reported.
"As you understand in diplomatic practice, there will be answers from the Russian side", said Yakovenko.
Twenty-three diplomats were expelled from the UK.
"The crisis in relations between Moscow and London has reached a new peak", it said.
But in a series of British media interviews early on Thursday, Johnson said the evidence of Russian guilt was "overwhelming" because only Moscow had access to the poison used and a motive for harming Sergei Skripal.
Asked about their colleague Detective Sergeant Nick Bailey, who remains in hospital after suffering exposure to the nerve agent, Pc Collins said: "Obviously our best wishes go to him".
"We share the UK assessment that there is no plausible alternative explanation, and note that Russia´s failure to address the legitimate request by the UK government further underlines its responsibility", the statement continued, speaking for the leaders of the U.S., France, and Germany.
"A growing concern in all of this dangerous and destabilizing activity is Russia", she said.
Foreign minister Sergey Lavrov claimed London was using it as a distraction from Brexit, describing the government as behaving in a "boorish" way.
The statement, issued by Downing Street, said: "The United Kingdom briefed thoroughly its allies that it was highly likely that Russia was responsible for the attack".
Moscow has vowed there will be a swift response to the expulsion of 23 of its diplomats by Britain.
US President Donald Trump said: "It certainly looks like the Russians were behind it. Something that should never, ever happen, and we're taking it very seriously".
But despite the warning from Moscow, Mr Trump expressed the United States' full support for Britain. All of us who are geographically in Europe are vulnerable to an aggressive Russia.
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