Prime Minister Theresa May says Britain will expel 23 Russian diplomats and halt high-level contacts as part of a package of measures against Moscow, which ignored a deadline to explain how a deadly chemical developed during the Cold War was used to poison a former Russian spy in the English city of Salisbury last week.
Speaking in Parliament after a national security council meeting on March 14, May said that Russia provided no credible explanation for the incident and "treated the use of a military grade nerve agent in Europe with sarcasm, contempt and defiance."
“There is no alternative conclusion, other than that the Russian state was culpable for the attempted murder" of Sergei Skripal, 66, and his daughter, Yulia, 33, "and for threatening the lives of other British citizens in Salisbury" including a police officer who is in serious condition.
Later on March 14, the United States voiced strong support for its British ally in an emergency session of the United Nations Security Council, backing up May's allegations of Russian involvement.
"The United States believes that Russia is responsible for the attack on two people in the United Kingdom, using a military-grade nerve agent," U.S. Ambassador Nikki Haley told the council.
In her comments, May condemned the "unlawful use of force by the Russian state against the United Kingdom” and said Britain "will freeze Russian state assets wherever we have the evidence that they may be used to threaten the life or property" of its citizens or residents.
May said the 23 diplomats, who were identified as "undeclared intelligence officers," will have one week to leave the country. The Russian Embassy in London called the decision a "hostile action" that is "totally unacceptable, unjustified, and shortsighted."
A Russian Foreign Ministry spokeswoman said later on March 14 on Russian TV that Moscow had received the list.
May said the move, which she described as the biggest expulsion of Russian diplomats from Britain in over 30 years, will degrade Russian intelligence capabilities in Britain for years to come. In 1985, London and Moscow engaged in mutual expulsions when 31 citizens from each country were sent packing following the defection to Britain of KGB agent Oleg Gordievsky.
May also said that Britain would suspend all planned high-level bilateral contacts with Russia, revoking an invitation for Foreign Minister Sergei Lavrov to visit, and that British ministers and the royal family would not attend the soccer World Cup in Russia this summer.
Furthermore, May said Britain would seek to strengthen its power to impose sanctions in response to the violations of human rights. "In doing so, we will play our part in an international effort to punish those responsible for the sorts of abuses suffered by Sergei Magnitsky," May said.
The Magnitsky Act, adopted by the United States in 2012, imposed visa bans and asset freezes on Russians alleged to be involved in the death of whistle-blowing accountant Magnitsky.
Sergei and Yulia Skripal were found unconscious on a bench outside a shopping mall in Salisbury on March 4. British authorities say they were exposed to a deadly chemical substance developed by the Soviet military that was part of a group of nerve agents known as Novichoks.
May had given Moscow a deadline of midnight on March 13 to explain how the rare nerve agent made its way to England.
Russia denies involvement and ignored the deadline, with Lavrov saying that Moscow was "not guilty" and that Britain was not following the proper procedures for reporting suspected chemical weapons attacks
"All the responsibility for the deterioration of the Russia-UK relationship lies with the current political leadership of Britain," the Russian Embassy to Britain said in a statement posted on its website after May's announcement on March 14.
Valentina Matvienko, the speaker of Russia's Federation Council -- the upper house of parliament -- said on March 14 that Moscow should react to Britain's actions in a fast, tough and reciprocal way. Matvienko also labelled British actions toward Russia a provocation.
Britain has called for an urgent meeting of the UN Security Council -- on which both Russia and Britain hold permanent seats -- to update members on the investigation into the poisoning, the Foreign Office said.
Along with the United States, the European Union and NATO also voiced support for Britain.
NATO's main decision-making body, the North Atlantic Council, expressed "deep concern at the first offensive use of a nerve agent" on alliance territory since NATO was founded in 1949.
In a statement, the allies called on Russia to answer Britain's questions in full about the Novichok nerve agent.
European Council President Donald Tusk said EU leaders would discuss the matter at its meeting next week, adding that the incident showed the need for "transatlantic unity".
In Geneva, the head of the British mission to the UN there, Julian Braithwaite, told the Human Rights Council that Russia’s "reckless behavior is an affront to all this body stands for."
Prior to Haley's remarks, Jason Mack, a first secretary at the U.S. mission in Geneva, said, "From Ukraine to Syria, and now the United Kingdom, Russia continues to be an irresponsible force of instability in the world,"
A few hours before May’s announcement, President Vladimir Putin's spokesman reiterated Russia's denial of involvement, saying that Moscow was in no way connected to the poisoning and would not accept "unfounded” accusations or ultimatums.
Spokesman Dmitry Peskov expressed hope that any measures by London will be based on "common sense," warning that punitive measures against Moscow will trigger a response. He did not elaborate.
Lavrov accused Britain of "acting out a political drama" to mislead the international community.
He argued that Russia had no motive to attack Skripal and said the poisoning could have been plotted by people or groups with an interest in spreading "Russophobic" sentiment.
Despite May's demand, Lavrov said that London has not sent an official request for information about the nerve agent involved in the attack.
He had earlier said that his country's requests to see samples of the nerve agent had been turned down.
Skripal, a retired Russian military intelligence colonel, was convicted by a Moscow military court in 2006 of "high treason" for passing secrets to Britain's Secret Intelligence Service.
He was one of four Russian prisoners released in 2010 in exchange for 10 Russian sleeper agents detained in the United States in one of the biggest spy scandals since the Cold War.
Police have confirmed that Sergei Skripal is a British citizen. Lavrov has said that Yulia Skripal has Russian citizenship.
With reporting by AFP, AP, Reuters, and Sky News