He repeated Moscow's position on the case, saying British allegations against Russian Federation were "absolutely boorish". Moscow responded to the ultimatum with scorn and sarcasm, ultimately blowing off May's demands.
The Western leaders said the use of the Novichok toxin was a clear breach of the Chemical Weapons Convention and worldwide law.
"This happened in the UK but it could have happened anywhere and we take a united stance against it", she said.
In the past days, she's sought support from worldwide allies and has spoken to US President Donald J. Trump, German Chancellor Angela Merkel and French President Emmanuel Macron.
Mr Trump said it was a "very sad situation" that the U.S. was taking "very seriously".
May has directly accused President Vladimir Putin, poised to win a fourth term in an election on Sunday, of being behind the attack.
The next move could come from Moscow. Labour Party leader Jeremy Corbyn said in the Guardian that it's possible that "Russian mafia-like groups", rather than the Russian state, were responsible.
Johnson defended the measures announced on Wednesday and suggested that there could be further consequences for wealthy Russians with assets in Britain.
At home, the British government has been under pressure from lawmakers and media to show it is getting tough on Russian Federation, with some experts saying that despite the rhetoric the response did not go far enough to bother Putin. "You got to keep your powder a little bit dry". Because we have suspicions that the truth about Yulia's and her father's conditions are being held from us.
Amber Alert issued for 2 Chicago area children
Her family said she left the state to get away from Washington, but the courts forced her to come back to IL with the children. Investigators believe 3-year-old Lynn Roby and 2-year-old Jordyn Washington are with their father, 40-year-old Lynn Washington.
Officials and pundits in Moscow have issued a steady stream of denials and counterclaims, a tactic that has continued through Thursday. The Kremlin said the British position was irresponsible and not backed up by evidence.
Britain, the United States, Germany and France jointly called on Russian Federation on Thursday to explain how the toxin came to be used on British soil.
They called on Russian Federation to provide a complete disclosure of the Novichok program to the Organisation for the Prohibition of Chemical Weapons in The Hague.
Mirzayanov revealed details of Russia's chemical weapons in the 1990s because he said he was afraid of their impact. Have you seen photos of the Skripal in the hospital? Both are reported to be in comas.
It's the latest escalation in the clash between the two nations over the use of a military-grade nerve agent against a former Russian spy who is now a British citizen.
That led to speculation that Tillerson's firing and his harsh words on Russian Federation ("we are outraged that Russian Federation appears to have again engaged in such behavior") may have been linked.
This morning Mrs May's government United Kingdom government's announced 48 million pounds of funding, for things like a new chemical weapons defence centre. A police officer was also exposed to the nerve agent and was hospitalized. But the alliance is engaged, Stoltenberg said.
Russian Federation is responsible for a "blurring of the line between peace, crisis and war", Stoltenberg said, calling the Kremlin's behavior "destabilizing and risky".
"I will announce the measures that we are going to take in the coming days", Macron told reporters during a visit to central France. He said it was "very unlikely" the Novichok used in Salisbury could have been lost or stolen in the years after the Soviet Union collapsed in 1991.
Speaking to the BBC earlier on Thursday, Foreign Secretary Boris Johnson said a sample of the nerve agent would be sent to the OPCW. Russian Federation has said it will reply in kind.
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