Theresa May expelled 23 Russian diplomats in the wake of a poisoning attack on an ex-spy on UK soil.
British Prime Minister Theresa May on Wednesday expelled 23 diplomats and suspended high-level contacts with Russia including for the World Cup, saying her government found Moscow "culpable" of the nerve agent poisoning of a former spy.
May told parliament that Russia had failed to respond to her demand for an explanation on how a Soviet-designed chemical, Novichok, was used in the English city of Salisbury on March 4.
At an emergency meeting of the UN Security Council in New York, the United States sided firmly with Britain, rejecting Moscow's claim that it was not involved in the attack on Sergei Skripal and his daughter.
"The United States believes that Russia is responsible for the attack on two people in the United Kingdom, using a military-grade nerve agent," US Ambassador Nikki Haley told an emergency council meeting held at Britain's request.
NATO allies have expressed their support for Britain following the first use of a nerve agent in Europe since World War II.
"There is no alternative conclusion other than that the Russian state was culpable for the attempted murder of Mr Skripal and his daughter," Ms May told parliament.
"This represents an unlawful use of force by the Russian state against the United Kingdom."
World Cup boycott
Ms May said 23 Russian diplomats believed to be intelligence officers must leave Britain within a week.
Britain also suspended all planned high-level contacts, including an invitation for Foreign Minister Sergei Lavrov to visit, but Ms May said she did not want to break off relations entirely.
She vowed to clamp down on Russians suspected of "hostile state activity", freezing assets for those in Britain and detaining those arriving at the border.
Neither members of the royal family nor ministers will attend the football World Cup in Russia later this year.
Alexei Sorokin, the chief of the World Cup organising committee, said the boycott would have "no impact on the quality of the tournament".
"It is every fan's choice whether to come or not," Mr Sorokin said.
Sam Greene, head of the Russia's Institute at King's College London, told AFP the expulsion of diplomats was a "standard thing to do" and would draw a mirror response from Moscow.
Mathieu Boulegue, a research fellow at Chatham House think tank, said the response was "relatively soft".
Russia threatened to expel British media, after suggestions from British politicians that its state-owned channel RT could have its licence reviewed in Britain.
'Choice for confrontation'
Ms May said on Monday it was "highly likely" Russia was behind the attack, which left Skripal and his daughter in critical conditions and a policeman also in hospital.
She said Moscow could be directly responsible or may have "lost control" of the nerve agent, and gave it until midnight local time on Tuesday to disclose details of the Novichok programme to the international Organisation for the Prohibition of Chemical Weapons (OPCW).
On Wednesday, she said Russia had responded with "sarcasm, contempt and defiance".
Moscow has said it is willing to cooperate but has accused Britain of failing to follow its own obligations for the investigation under OPCW rules, complaining that its request for samples of the nerve agent has been rejected.
"The British government made a choice for confrontation with Russia," the foreign ministry said, accusing London of pursuing a political agenda.
At the United Nations, Russian Ambassador Vassily Nebenzia repeated Moscow's denials and suggested the attack was a provocation aimed at tarnishing Russia's image ahead of the World Cup and elections.
"Russia had nothing to do with this incident," Mr Nebenzia told the council and again demanded proof of a link to Russia.
"We have nothing to fear. We have nothing to hide."
Ms May has spoken to US President Donald Trump, French President Emmanuel Macron and German Chancellor Angela Merkel in recent days to rally international support.
In a phone call late on Tuesday, Mr Trump and Ms May "agreed on the need for consequences for those who use these heinous weapons in flagrant violation of international norms", the White House said.
In a joint statement by its 29 member states, the US-led NATO alliance said the attack was a "clear breach of international norms and agreements" and called on Russia to fully disclose details of the Novichok programme.
EU Council President Donald Tusk offered his "full solidarity" and indicated the issue would be on the agenda of next week's summit in Brussels.
British experts say Skripal, 66, and his 33-year-old daughter were poisoned with a nerve agent from a broad category known as Novichok, which was developed by the Soviet Union during the late stages of the Cold War.
The Russian chemist who first revealed the existence of Novichok, Vil Mirzayanov, said "only the Russians" developed the Novichok agents.
The case has drawn parallels with the 2006 death by radiation poisoning of former Russian agent and Kremlin critic Alexander Litvinenko, which Britain blamed on Moscow.