British Prime Minister Theresa May said Monday that the recent poisoning of a former spy and his daughter in the city of Salisbury was "highly likely" tied to Russia.
May, speaking to British lawmakers, called the poisoning a "reckless and despicable act" and said "it is highly likely that Russia was responsible for the attack."
The prime minister said the poison was a "military-grade nerve agent of a type developed by Russia."
Although May's government had been reluctant to point the finger without adequate evidence, given the myriad similarities between this case and the poisoning of former Russian spy Alexander Litvinenko in 2006, there had been rampant speculation that Moscow was responsible and that firm action needed to be taken.
Sergei Skripal, 66, is a retired Russian military intelligence officer who was convicted and jailed for being a double agent for the British intelligence service MI6. He was released in 2010 during a prisoner swap and had been given refuge in Britain, where he reportedly kept a low profile but was not using a different identity.
Russia denies any involvement in the poisoning of Skripal and his daughter, Yulia, 33.
But May said it is clear that Skripal and his daughter were poisoned with part of a group of nerve agents known as Novichok.
She said that based on the assessment of leading experts and on "our knowledge that Russia has previously produced this nerve agent and would still be capable of doing so, Russia's record of conducting state-sponsored assassinations and our assessment that Russia views some defectors as legitimate targets for assassinations, the government has concluded that it is highly likely that Russia was responsible for the act against Sergei and Yulia Skripal."
May said there were two plausible explanations: "Either this was a direct act by the Russian state against our country. Or the Russian government lost control of its potentially catastrophically damaging nerve agent and allowed it to get into the hands of others."
Whether Britain's response would include sanctions against Russia remained unannounced Monday. May said the Russian ambassador had been called upon to answer questions on how the nerve agent ended up being used on British soil.
Russian President Vladimir Putin, meanwhile, advised Britain to get things clear with the poisoning before discussing the matter with officials from his country, Russia's Tass news agency reported.
Putin spokesman Dmitry Peskov said the Skripal case had nothing to do with Moscow.
"In any case, this is not our affair at all," Peskov said. "The aforesaid Russian citizen had worked for one of Britain's secret services. The incident occurred in British territory. By all means this is not an affair that concerns Russia, let alone Russia's leadership."
White House Press Secretary Sarah Huckabee Sanders said the U.S. condemned the use of a nerve agent in the United Kingdom. She did not acknowledge Russia as the suspected source of the attack.
"The attack was reckless, indiscriminate and irresponsible," she told reporters. "We offer the fullest condemnation, and we extend our sympathy to the victims and their families, and our support to the U.K. government."
Secretary of State Rex Tillerson expressed confidence in Britain's investigation and its assessment that Russia was probably responsible for the poison attack.
"Russia continues to be an irresponsible force of instability in the world, acting with open disregard for the sovereignty of other states and the life of their citizens," Tillerson said in a statement.
It was unclear why it took a week for public health warnings to be issued to the approximately 500 people who visited the restaurant or the pub where the former spy and his daughter spent time March 4 before being found slumped unconscious on a bench in the quiet cathedral city of Salisbury.
On Sunday, the government issued an advisory saying any member of the public who frequented the restaurant Zizzi or the Mill pub should wash their clothes, double bag any items for dry cleaning and wipe any jewelry or cellphones with wet wipes to prevent possible contamination.
It was described as a purely precautionary measure, but residents reacted with a mixture of apathy and incredulity to the fact that authorities took a week to provide that advice.
"Why it took them so long to release that advice is really strange," said Sam Peters, 40, who lives a few miles outside the town center. "You'd think something like this would trigger advice; it's an obvious common-sense thing to do."
A table inside Zizzi, where Skripal and his daughter ate lunch, has been destroyed after traces of poison were found on it, officials said.
Ben Smith, manager of the Avon Brewery a short distance from the Mill, said he was not concerned and felt the investigation was being handled well.
Smith said business was noticeably down compared with the same week a year ago.
"This certainly is something that hasn't happened here before and never in a million years would you think it would happen," he said. "Maybe that's why there was a slow response time."
Police are treating the case as an attempted murder. Skripal and his daughter remain in critical condition in a hospital; a police officer who first responded to the incident and subsequently became sick is now listed in stable condition and is sitting up in bed and talking, officials said.
The night before May's comments, a leading Russian television news anchor said Britain may have planned the poisoning of Skripal and his daughter as a way to fuel more "Russophobia" in Britain and spark calls for a boycott of the World Cup soccer tournament. Russia is hosting that event, which starts in June.
"It's the perfect special operation," Dmitry Kiselyov said on his Sunday evening program, "Vesti Nedeli," on the state channel Russia 24.
Boyle is a special correspondent. Special correspondent Sabra Ayres in Krasnodar, Russia, and Times staff writer Tracy Wilkinson in Washington contributed to this report.
8:25 p.m.: This article was updated with a comment by Secretary of State Rex Tillerson.
2:15 p.m.: This article was updated with reaction from the White House.
1:25 p.m.: This article was updated with reaction from Russian officials and additional details.
10:40 a.m.: This article was updated with Prime Minister Theresa May's comments Monday.