UK and its allies say Russia was behind the poisoning of Skripal and his daughter, who remain in a critical condition in Salisbury.
Moscow: International pressure mounted on Russia's Vladimir Putin over 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.
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 on Wednesday after a phone call between the pair.
However the comments came a day after Trump called 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.
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.