British police say they believe aand his daughter were poisoned with a nerve agent. Metropolitan Police counterterrorism chief Mark Rowley said Wednesday the attack on Sergei Skripal and his daughter Yulia on Sunday is being treated as attempted murder.
He says police believe they were specifically targeted.
They are inin a hospital.
Rowley says a police officer who treated them when they collapsed in Salisbury on Sunday is also in serious condition.
Chief medical officer Sally Davies said the poisoning posed a "low risk" to the general public.
Skripal, a former colonel in Russia's GRU military intelligence service, was convicted in 2006 of spying for Britain and imprisoned. He was freed in 2010 as part of a widely publicized spy swap in which the U.S. agreed to hand over 10 members of a Russian sleeper cell found operating in America in return for four Russians convicted of spying for the West.
He and his daughter were found collapsed on a bench near a shopping mall Sunday in Salisbury, 90 miles southwest of London. Police believe they were exposed to a substance, and a British military research facility is thought to be conducting tests to determine what it is.
Foreign Secretary Boris Johnson told lawmakers Tuesday that if Moscow is shown to have been involved in the Skripal case, the government would act - possibly downgrading England's participation in this year's soccer World Cup in Russia.
While police say they are keeping an open mind about the case, it has reminded Britain of the 2006 poisoning of former spy Alexander Litvinenko.
A British inquiry into his death found that Russian agents poisoned him by lacing his tea with radioactive polonium-210 and that the killing was probably approved by President Vladimir Putin. Russia has denied any involvement in Litvinenko's death, and this week said it wasn't involved in Skripal's collapse.
Litvinenko's widow, Marina, wrote Wednesday in the Times of London that her husband's case made clear to Britain's emergency services that they need to act quickly when "someone suddenly falls mysteriously ill."
"I am happy my story has raised awareness about the potential danger posed by Moscow, and this could help to save somebody's life," she wrote in an opinion piece.
British counterterrorism specialists have taken control of Skripal's case from local police trying to unravel the mystery of what happened. The matter has not been declared a terrorist incident.
As speculation swirled, experts watching the matter say the circumstances so far suggest that it is unlikely that a radioactive substance was responsible, as was the case with Litvinenko.
Malcolm Sperrin, the former head of medical physics at the Royal Berkshire Hospital, said it would normally take time for a radioactive dose to become evident. Skripal and his daughter were seen on CCTV walking in the city only a short time before they became ill.
"If you were to give a dose of something radioactive, that could take many weeks" to become clear, he said - unless it were highly radioactive. In that case, those who came into contact with you would also be affected.
Most of the people who initially responded to the attack have been released from the hospital. Beyond that, there are too many unknowns to identify the chemical from arm's length, he said.
"There are a lot of very exotic chemicals," he said.