Foreign ministry official Vladimir Yermakov said London itself could have been behind the poisoning of Skripal.

International pressure mounted on Russia's Vladimir Putin over the the Cold-War style poisoning of a spy on British soil, as an ugly war of words took a stinging new turn with comparisons to Hitler in the 1930s.

US President Donald Trump agreed with his French counterpart Emmanuel Macron “on the need to take action to hold Russia accountable” following the attempted murder of former double agent Sergei Skripal and his daughter Yulia.

Mr. Trump expressed “solidarity with the United Kingdom in the wake of Russia's use of chemical weapons against private citizens on British soil,” the White House said Wednesday after a phone call between the pair.

However the comments came a day after Mr. Trump called Mr. Putin to congratulate him on his re-election to the Russian presidency, drawing criticism for failing to condemn the poisoning or even mention the scandal.

Britain and its allies say Russia was behind the attack on Skripal and his daughter, who remain in a critical condition after being poisoned in the English town of Salisbury with what London says is a Soviet-designed nerve agent.

But Moscow has angrily rejected the claims and on Wednesday hosted a televised briefing for foreign diplomats at which a senior official mocked Britain's “island mentality” and “Russophobia”.

Foreign ministry official Vladimir Yermakov said London itself could have been behind the poisoning of Skripal, a former Russian officer who sold secrets to Britain and moved there in a 2010 spy swap.

“The British authorities are either unable to ensure protection from such a... terrorist attack on its territory, or they directly or indirectly — I am not accusing anyone of anything here — directed the attack on a Russian national,” he said.

Mr. Yermakov — the head of the ministry's non-proliferation and arms control department — alternated between tough talk and quips and said in response to a question from a British official: “I am ashamed for you”.

The diplomat rejected claims the chemical weapon “Novichok” was used in the attack, saying it would have killed people on the spot and suggested that Washington might have also had a hand in the incident.

Hitler comparisons

The deepening row has already seen Britain throw out 23 Russian diplomats, prompting a tit-for-tat response from Moscow which also closed the British Council cultural institute in Russia.

British Foreign Secretary Boris Johnson said Wednesday that Russia had wanted to send "a sign" with the nerve agent attack on Skripal to warn defectors that they cannot escape Moscow's power.

In an appearance before a committee of MPs in London, Mr. Johnson said Russia chose a target in Britain because of London's record of "calling out" Moscow's abuses.

“I think the reason that they picked the United Kingdom is very simple, it's because this is a country that does have that particular set of values, it does believe in freedom, and in democracy and in the rule of law, and has time and again called out Russia over its abuses of those values.”

Mr. Johnson also agreed with an MP who suggested Putin would exploit the 2018 football World Cup in Russia as Nazi dictator Adolf Hitler did the Berlin Olympics.

Hitler wanted the 1936 Games to be a symbol of Aryan supremacy and famously refused to shake hands with American star Jesse Owens, the black track and field athlete who won four gold medals in Berlin.

“I think the comparison with 1936 is certainly right,” Mr. Johnson said, envisaging Mr. Putin “glorying in this sporting event”.

The spokeswoman for Russia's foreign ministry Maria Zakharova said in a Facebook post that “(Johnson) is poisoned by hatred and malice, a lack of professionalism and therefore rudeness”.

“It's terrible to think that this man represents the political leadership of a nuclear power,” she said.

'Drivel, rubbish, nonsense'

Mr. Putin has dismissed allegations of Moscow's involvement as “drivel, rubbish, nonsense”, while Foreign Minister Sergei Lavrov on Wednesday urged the British government to “respond calmly” to the Skripals' attempted murder.

“If the British government continues taking some anti-Russian measures, we will hit back under the principle of reciprocity,” he said in Japan.

“Overall, there is no doubt that the British leadership has knowingly chosen to undermine the British-Russian relationship.”

Britain says only Russia had the capability, motive and intent to be behind the attack.