Update - 1.52pm: Russia's ambassador to the UK Alexander Yakovenko quoted foreign minister Sergey Lavrov as saying Britain's "failure to co-operate" on the Skripal case was a "major violation of the chemical weapons convention".
"The situation will rest on the conscience of those who started this reckless gamble," Mr Lavrov added.
Russian foreign minister Sergei Lavrov said: "Russia is not guilty, Russia is ready to co-operate in line with the Organisation for the Prohibition of Chemical Weapons convention if the United Kingdom gets round to - and deigns to - fulfilling its international legal obligations in line with the document."
12.32pm: Nato and Poland back UK as Russia claims 'anti-Russian campaign' around spy poisoning
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."
The poisoning of Sergei and Yulia Skripal provided the UK authorities with a "possibility to launch this anti-Russian campaign," said Mr Yakovenko, adding: "This is a scenario that was written in London but it's a short-sighted scenario because, in the long run, Britain will have to explain what is behind all these things in Salisbury."
He added: "Nobody saw even the pictures of these people in a hospital, whether they are alive or maybe they are in good health. Nobody talked to the doctors. There is absolutely no transparency in the case.
"We want to clarify all the questions behind this provocation."
In a separate interview with Rossiya 24 TV, Mr Yakovenko said that Russia would exert maximum pressure on the UK over the situation.
Nato's secretary general has voiced the strong support of the military alliance's 29 members for the UK in the current row with Russia over the Salisbury poisoning.
Jens Stoltenberg was speaking a day after National Security Adviser Sir Mark Sedwill briefed Nato states at the North Atlantic Council in Brussels on the UK's intelligence case for viewing Russia as responsible for the attack on Sergei Skripal.
Mr Stoltenberg told BBC Radio 4's Today programme: "We have no reason to doubt the findings and assessments made by the British Government."
And he added: "The Nato allies express strong political support for the UK. The UK is not alone. All allies stand in solidarity with the UK."
Mr Stoltenberg said: "I am absolutely certain that Russia has underestimated the resolve and unity of Nato allies."
Polish foreign minister Jacek Czaputowicz said: "We are sure that it is Russian state which is involved in this attempt. It is certain."
The foreign minister said: "As far as sanctions are concerned Poland would support such action.
"I think the international community has to mobilise around this case in order to demonstrate to Russia decisiveness and there is no acceptance to the breach of international law."
7.26am: Vladimir Putin expected 'softer' reaction to poisoning, says former Georgian president
Former Georgian president Mikheil Saakashvili has suggested that Russia attempted to assassinate a spy in the UK because Vladimir Putin expected the reaction would be "softer" than other nations.
Mr Saakashvili suggested a similar move would not have been made in the US as it may have triggered "unpredictable reactions" from president Donald Trump.
Speaking to Sky News, the avowed enemy of Mr Putin said wealthy Russians had an established foothold in London and "nobody would risk long-term damage to relations because there are too much powerful interests inside UK at play".
He said: "I think that for some reason Russia believed that the UK would be softer on Russia than, say, the United States.
"I don't imagine him doing the same now on Trump's America, because that might trigger unpredictable reactions from Trump.
"For some reason he believes there will not be the same reaction from the UK long term."
Mr Saakashvili said British Prime Minister Theresa May's swift and no-nonsense response had made her appear "as someone strong and resolute".
However Mr Putin has long seen indifference to his transgressions from the West and has been emboldened as a result, he said.
"Moving the red line, crossing it and moving it again. He has been warning about moving it, hearing his own voice, seeing the lack of reaction from the West and moving it further."
Mr Saakashvili was president of Georgia from 2004-13, during which time the country suffered a brief conflict with Russia in 2008.
He left the former Soviet republic when his presidency ended and eventually went to Ukraine, where he was appointed governor of the Odessa region.
In January he was sentenced in absentia to three years in prison for abusing his power in pardoning four policemen convicted of killing a banker.
He is currently living in exile in the Netherlands.