MOSCOW (AP) -- Russia on Saturday announced it is expelling 23 British diplomats and threatened further measures in retaliation in a growing diplomatic dispute over a nerve agent attack on a former spy in Britain.
Britain's government said the move was expected, and that it doesn't change the British conviction that Russia was behind the poisoning of ex-agent Sergei Skripal and his daughter in the British city of Salisbury. Prime Minister Theresa May said Britain will consider next steps in the coming days alongside its allies.
The Russian Foreign Ministry ordered the 23 diplomats to leave within a week. It also said in a statement that it is ordering the closure of the British Council, a government-backed organization for cultural and scientific cooperation, and that it is ending an agreement to reopen the British consulate in St. Petersburg.
The announcement followed on the heels of Britain's order this week for 23 Russian diplomats to leave the U.K. because Russia was not cooperating in the case of the Skripals, both found March 4 poisoned by a nerve agent that British officials say was developed in Russia. The Skripals remain in critical condition.
Britain's foreign secretary accused Russian President Vladimir Putin of personally ordering the poisoning of the Skripals. Putin's spokesman denounced the claim.
The Russian statement said the government could take further measures if Britain takes any more "unfriendly" moves toward Russia. British Ambassador Laurie Bristow was called to the Foreign Ministry Saturday to be informed of the moves.
"We will always do what is necessary to defend ourselves, our allies and our values against an attack of this sort, which is an attack not only on the United Kingdom, but upon the international rules-based system on which all countries, including Russia, depend for their safety and security," Bristow told reporters after being informed of the expulsions.
"This crisis has arisen as a result of an appalling attack in the United Kingdom, the attempted murder of two people, using a chemical weapon developed in Russia and not declared by Russia at the Organization for the Prohibition of Chemical Weapons, as Russia was and is obliged to do under the Chemical Weapons Convention," he added.
Russian Foreign Ministry spokeswoman Maria Zakharova on Saturday denied that Russia or the Soviet Union had ever developed the nerve agent Novichok that Britain said was used to poison the Skripals.
A Russian scientist disclosed details of the secret program in the 1990s, and later published the formula for Novichok. But Russia maintains it has never made them.
Speaking on Russia-24 television, Zakharova said Britain's angry reaction is connected to the war in Syria. She said Britain is taking a tough line because of frustration at recent advances of Russian-backed Syrian government forces against Western-backed rebels.
Russia argues that it has turned the tide of the international fight against Islamic State extremists by lending military backing to Syria's government. With Russian help, Syrian forces have stepped up their offensive on rebel-held areas in recent days, leaving many dead.
The British National Security Council will meet early next week to consider the next steps after Saturday's expulsion announcement.
The Foreign Office says "Russia's response doesn't change the facts of the matter — the attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian State was culpable."
The British Council said in a statement it is "profoundly disappointed" at its pending closure. The organization has been operating in Russia ever since the fall of the Soviet Union.
"It is our view that when political or diplomatic relations become difficult, cultural relations and educational opportunities are vital to maintain on-going dialogue between people and institutions," it said.
British police appealed Saturday for witnesses who can help investigators reconstruct the Skripals' movements in the crucial hours before they were found unconscious.
Western powers see the attack as the latest sign of alleged Russian meddling abroad. The tensions threaten to overshadow Putin's expected re-election Sunday for another six-year presidential term.
Meanwhile new tensions have surfaced over the death this week of a London-based Russian businessman, Nikolai Glushkov. British police said Friday that he died from compression to the neck and opened a murder investigation.
Russia also suspects foul play in Glushkov's death and opened its own inquiry Friday.
British police said there is no apparent link between the attack on Glushkov and the poisoning of the Skripals, but both have raised alarm in the West at a time when Russia is increasingly assertive on the global stage and facing investigations over alleged interference in the Donald Trump's election as U.S. president.