Moscow has demanded an open session of the UN Security Council on Thursday over Britain’s claim that it is “highly likely” Russia was behind the poisoning.
It comes after Russia lost a vote at the global chemical weapons watchdog, where the country called for its experts to join the probe into the attack.
Britain said the demand was a sign the federation was “nervous” of what the inquiries will find.
Tensions between the two countries have risen after the head of the Porton Down military research facility told Sky News scientists had not verified Russia as the source of the novichok used on former spy Sergei Skripal and his daughter Yulia.
Russian President Vladimir Putin seized on the comments as he accused the UK of launching an “anti-Russian campaign”.
Foreign Secretary Boris Johnson is facing calls for an inquiry into whether he “misled the public” after he appeared to suggest Porton Down was in “no doubt” the nerve agent in Salisbury originated in Russia.
The Foreign Office later deleted a Twitter post that claimed UK experts had “made clear” the substance was “produced in Russia”.
Labour has called on the Prime Minister to launch an investigation into whether Mr Johnson broke the ministerial code.
“The Foreign Secretary has some serious questions to answer over whether he misled the public, but is instead trying to deflect criticism with his characteristic bluff and bluster,” Labour’s shadow Cabinet Office minister Jon Trickett said.
Mr Johnson criticised Jeremy Corbyn for “playing Russia’s game” after the Labour leader accused him of “exaggeration” over the evidence.
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Meanwhile, The Times reported that UK security services have high degree of confidence that they have pinpointed the location of the Russian laboratory that manufactured the nerve agent used in the attack.
A Whitehall source told the newspaper: “We knew pretty much by the time of the first Cobra (the emergency co-ordination briefing that took place the same week) that it was overwhelmingly likely to come from Russia.”