- Video report by ITV News Correspondent Emma Murphy
It is "overwhelmingly likely" that Russian president Vladimir Putin ordered the use of a nerve agent in the attack on ex-spy Sergei Skripal in Britain, Foreign Secretary Boris Johnson has said.
Mr Johnson's decision to place blame for the attack in Salisbury on Mr Putin personally came as Britain awaited Moscow's response to the expulsion of 23 of its diplomats.
The Foreign Secretary's comments earned a scathing rebuke from Mr Putin's spokesman Dmitry Peskov, who said: "We have said on different levels and occasions that Russia has nothing to do with this story. Any reference or mentioning of our president is nothing else but shocking and unpardonable diplomatic misconduct."
Visiting the Battle of Britain Bunker museum in Uxbridge, the Foreign Secretary thanked allies for their support, adding: "It is overwhelmingly clear that this was directed by Russia and we await a serious response from the Russians to that global condemnation.
"I've been very impressed, overwhelmed, by the solidarity countries around the world have shown."
Russia's ambassador in London Alexander Yakovenko suggested that the British Government was making allegations against Moscow as part of an "anti-Russian campaign" to divert attention from Brexit.
Mr Yakovenko told RT television: "In order to divert attention from Brexit, the UK has to present something to the public to move (the focus) a little bit to the other side."
Mr Johnson told reporters on Friday that Britain's anger is directed against "Putin's Kremlin" not the Russian people.
He said: "Our quarrel is with Putin's Kremlin, and with his decision, and we think it overwhelmingly likely that it was his decision to direct the use of a nerve agent on the streets of the UK, on the streets of Europe, for the first time since the Second World War. That is why we are at odds with Russia."
Russia will expel British diplomats in a worsening global standoff over the poisoning of a former Russian spy with a nerve agent.
Foreign Minister Sergey Lavrov did not confirm when the diplomats would be expelled and how many.
But he accused Britain of violating international law and said Britain's defence minister "lacks education."
The move comes after a joint statement was issued by US President Donald Trump, Germany's Angela Merkel and France's Emmanuel Macron endorsing Theresa May's conclusion that it was "highly likely" Russia was behind the attack on Sergei Skripal and his daughter Yulia in Salisbury.
The source of the nerve agent used which Britain says is Soviet-made Novichok is unclear.
Russia denies being the source of the nerve agent, suggesting it could have been another country, and has demanded Britain share samples collected by investigators.
Lavrov said Russia will "of course" expel British diplomats and that he hopes the Skripals recover soon so light can be shed on what happened.
Lavrov also lashed back at British Defence Secretary Gavin Williamson for saying Russia "should go away and shut up".
"Perhaps he also wants to go down in history with some loud statements," he said. "I don't know, perhaps he lacks education." Lavrov told a news conference after talks on Syria's war with his Iranian and Turkish counterparts.
The mounting tensions come as Russians prepare to hand President Vladimir Putin a new term in an election Sunday.
Moscow is also plotting a response to the United States after Donald Trump's administration imposed sanctions on Russians allegedly involved in interfering with the 2016 US elections and cyber-attacks.
The attack on the Skripals was highlighted by the US Treasury as one of the justifications for the tougher line against Moscow.
The US treasury department said the use of a military-grade nerve agent in the Salisbury incident "further demonstrates the reckless and irresponsible conduct of its (Russia's) government".
The sanctions prompted a swift threat of retaliation from the Russian government, which said a response was already being prepared.
President Vladimir Putin had a meeting with his security council on Thursday to consider UK-Russia relations.
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 Daily Telegraph reported on Thursday that the nerve agent used in the attack could have been planted in Yulia Skripal's suitcase during a recent trip to Moscow.
The newspaper said senior intelligence sources believe an item of clothing, cosmetics or a gift could have been laced with the Novichok toxin.
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.
He warned Mrs May not to "rush way ahead of the evidence" - highlighting the way international crises such as the Iraq War had seen "clear thinking" overwhelmed by "emotion and hasty judgments".
Writing in the Guardian he warned against a "new Cold War" of "escalating arms spending, proxy conflicts across the globe and a McCarthyite intolerance of dissent".
Confirming Labour's support for Mrs May's actions, Mr Corbyn said: "We agree with the Government's action in relation to Russian diplomats."
But he added: "Measures to tackle the oligarchs and their loot would have a far greater impact on Russia's elite than limited tit-for-tat expulsions."
Mr Corbyn said that Mrs May was right on Monday to identify two possibilities for the source of the nerve agent - either Russia authorised the attack or had lost control of the Novichok substance.
"If the latter, a connection to Russian mafia-like groups that have been allowed to gain a toehold in Britain cannot be excluded," he said.
The Labour leader, who opposed the 2003 invasion of Iraq, added: "In my years in parliament I have seen clear thinking in an international crisis overwhelmed by emotion and hasty judgments too many times.
"Flawed intelligence and dodgy dossiers led to the calamity of the Iraq invasion."
Scotland Yard Assistant Commissioner Neil Basu, who heads up the national counter-terror police network which is leading the Salisbury investigation, appealed for anyone with information about the "despicable" and "appalling" attack to come forward.