UK Prime Minister Theresa May has announced a series of measures against Moscow including the expulsion of 23 Russian diplomats.
Her statement to Parliament came after the UK's deadline for Moscow to explain how a Russian nerve agent was used on British soil expired.
She set the Tuesday midnight ultimatum saying it was "highly likely" Russia was behind the attack.
May's statement on steps against Russia - the main points:
- The UK concluded it was highly likely Russia was responsible for the poison attack. Either it was a direct attack against Britain or it had lost control of a military grade nerve agent
- Moscow's reponse demonstrated complete disdain for the gravity of events. It acted with sarcasm, contempt and defiance
- Russian state guilty of attempted murder of Sergei Skripal and his daughter, and threatening the lives of UK citizens including Detective Sergeant Nick Bailey (the policeman affected)
- Unlawful use of force by Russia against the UK follows a well-established pattern of aggression
- UK must come together with allies to defend security, stand up for values and send a clear message
- UK is expelling 23 Russian diplomats believed to be undeclared intelligence officers. They have one week to leave - the biggest single expulsion for 30 years
- Russian intelligence activity will thus be downgraded
- UK will urgently develop proposals for new legal powers against hostile state activity
- To include the power to detain suspects at UK borders (currently possible only regarding terrorism)
- UK will seek new powers to impose sanctions in response to human rights abuses
Checks to be increased on private flights, customs and freight
Russian state assets to be frozen if they are proven to threaten the life or property of UK citizens
With National Crime Agency government will continue to act against serious criminals and corrupt elites
Not in UK's interest to break off all dialogue but relationship with Russia can't be the same
High level bilateral contacts to be suspended; invitation to Foreign Minister Sergei Lavrov to be withdrawn; no ministers or Royal Family members will attend football World Cup in Russia
Earlier on Wednesday, a government source said Russia's ambassador had been summoned to the Foreign Office, Reuters reported.
Britain has called for an urgent meeting of the United Nations Security Council to update members on the investigation, the Foreign Office said. It has posted a video on Twitter listing cases of alleged Russian aggression over the past decade.
Meanwhile forensic teams continue to collect evidence in Salisbury, the site of last week's attack on former Russian agent Sergei Skripal and his daughter Yulia.
Russia denies charge
The Russian embassy in London described the steps announced by Theresa May as "unacceptable, unjustified and short-sighted". In a series of earlier tweets, the embassy rubbished the charge and said it would not cooperate unless the UK provided a sample of the toxin. It said any punitive measures would bring retaliation.
Russia's Foreign Minister Sergei Lavrov had not accepted an invitation to visit Britain, a ministry spokeswoman said on Wednesday in response to May's statement. The ministry accused Britain of choosing confrontation over cooperation when handling the case.
Earlier, Lavrov said no progress had been made towards resolving a standoff with London. He added that Russia would be ready to provide Britain with a response within 10 days if London submitted an official request, in line with the Chemical Weapons Convention.
"Instead of submitting such a request, Britain has continued to stage a political performance," he said, rejecting British claims that only Russia had a motive to target Skripal.
May has been the gathering the support of international allies for the UK government's action against Russia. She said she had spoken to President Trump, Chancellor Merkel and President Macron in the past 24 hours.
After a phone call with May before her statement to Parliament, President Trump said "the US was with the UK all the way."
Angela Merkel said the European Union would present a common stance over the nerve gas attack. "We take the findings of the British government very seriously," she told German broadcaster ARD, noting that European leaders would meet next week. "We will present a common European view here."
The German leader cited NATO, which on Wednesday called on Russia to give Britain "complete disclosure" of the Soviet-era nerve agent used in the attack on Skripal.
A French government spokesman said Paris was awaiting proof before deciding if it would act in solidarity with London.
Theresa May said the Organisation for the Prohibition of Chemical Weapons (OPCW) had been notified of Britain's findings and would verify its analysis of the substance used in the attack.
The poisoning of Sergei Skripal has been likened to the murder of ex-KGB agent Alexander Litvinenko, a critic of Vladimir Putin, who died in London in 2006 after drinking tea laced with radioactive polonium 210. A public inquiry concluded that the Russian president had probably ordered the killing.
Four Russian diplomats were expelled afterwards, to criticism that the response was too weak. Moscow refused to extradite the two Russians identified by Britain as the killers.