Russia has accused Britain of deliberate concealing evidence in the escalating war of words over the Salisbury nerve agent attack.
The Russian foreign ministry head of non-proliferation and arms control insisted Moscow bore no responsibility for the incident and dismissed British demands for an explanation as "absurd".
At a "briefing" for foreign diplomats in Moscow, Vladimir Yermakov questioned whether the incident, which left former Russian double agent Sergei Skripal and his daughter, Yulia, fighting for their lives even involved a nerve agent.
"All the facts are being concealed intentionally and the real evidence could (have) vanished. This has happened before in Great Britain, repeatedly," he said.
However, giving evidence to MPs, Foreign Secretary Boris Johnson said the trail of evidence led "inexorably" to the regime of Russian President Vladimir Putin.
Mr Johnson said: "As we saw in the case of the murder of Alexander Litvinenko, the trail of responsibility for such assassinations and assassination attempts does lead inexorably back to the Kremlin."
Britain expelled 23 Russian diplomats after military scientists at Porton Down concluded the Skripals had been poisoned by a Russian made Novichok nerve agent and the Kremlin then failed to respond to Theresa May's demand for an explanation.
The Russians in turn announced the expulsion of 23 British diplomats as well as the closure of the British Council and the British consulate in St Petersburg.
Mr Yermakov complained that the Russians had been denied consular access to Ms Skripal, who remains a Russian citizen, and said that it was up to the UK authorities to explain what had happened.
"This took place on the territory of Great Britain," he said.
"The simple logic here tells us there are two possible options: the British authorities are either unable to insure protection against such terrorist acts on their territory or they themselves directly or indirectly, I am not accusing anyone of anything, have directed this attack against a Russian citizen.
"There is simply no other third option here. In these circumstances requiring any explanations from the Russian side is simply absurd."
He added: "It is becoming more and more obvious that this attack against the Skripals in Salisbury is most probably a blatantly framed illegal adventure.
"Only one thing is clear, Russia has nothing to do with this. We do not benefit from it in any way."
But appearing before the Commons Foreign Affairs Committee Mr Johnson said: "I think it is our view that when it comes to the use of a Novichok type nerve agent in Salisbury to attempt to assassinate somebody who had been identified by the Russian state as a target for liquidation, not long after President Putin himself has said that such people would choke on their own 30 pieces of silver or deserve to be poisoned, no matter how exactly it came to be done, the pathway, the chain of responsibility, seems to me to go back to the Russian state and those at the top."
Asked what Mr Putin's motive for attacking Mr Skripal might be, Mr Johnson said: "I think first of all it was a sign that President Putin, or the Russian state, wanted to give to potential defectors in their own agencies that this is what happens to you if you decide that you support a country with a different set of values, such as our own.
"You can expect to be assassinated.
"The reason why they picked the UK is very simple. It is because this is a country that does have that particular set of values, that does believe in freedom and democracy and the rule of law and has time and again called out Russia over its abuses of these values."