LONDON — A British police official on Thursday updated the number of people who sought treatment after a nerve agent attack on an ex-Russian spy, saying "around 21" had been given medical help and support.
Only three people remain hospitalized after the poisoning Sunday in the southern English city of Salisbury — ex-spy Sergei Skripal, his daughter and a British police officer who tried to help them. Health officials insist there has been a low risk to the public.
Authorities haven't said who launched the attack, but U.K. officials have warned of a strong response if the Russian government is found to be responsible.
"Multiple people have been treated, around 21 people, including the man and the woman found on the bench," Wiltshire acting police chief Kier Pritchard told Sky News, referring to Skripal and his daughter, who were found unconscious.
Pritchard said that of the new total, "a number" of them got hospital treatment including blood tests, support and advice. Previously, authorities had said only that "several" people had sought treatment.
Police haven't provided details on the nerve agent that was used, and the ex-spy and his daughter remain in critical condition.
British Home Secretary Amber Rudd said whoever is behind the attack is guilty of a "brazen and reckless act." She said Britain would respond strongly when it is clear who's to blame.
She said that enormous resources were being used to determine who poisoned Skripal, 66, and his 33-year-old daughter Yulia. They were found unconscious on a bench, triggering a police inquiry headed by counterterrorism detectives.
A police officer who came to their aid is hospitalized in a serious condition, though he is conscious and talking, Rudd said. He was identified Thursday as Sgt. Nick Bailey.
"The use of a nerve agent on British soil is a brazen and reckless act," Rudd told Parliament. "This was attempted murder in the most cruel and public way."
The Russian Embassy in London, which has mocked other British politicians for suggesting Russian involvement, tweeted that it agreed with Rudd: "First evidence then conclusions on Mr. Skripal's case. Responsible political approach."
Police have refused to publicly speculate on who is behind the attack, but many experts have focused on Russia because of the similarity to the 2006 killing of another former Russian spy who was poisoned in London with radioactive polonium-210.
"Russia does seem like the most likely story, given what we know both of the background of this case ... given the track record in the state of the relationship, the fact that we have seen things like this before," Sam Greene, director of the Russia Institute at King's College London, told Sky News.
But Greene said that even if the attack was planned in Russia, it may not have been ordered by the Kremlin.
"A lot of these things are being done by people operating at sort of an arm's length's distance from the command and control structure," Greene said.
A public inquiry found that Russia was responsible for killing Alexander Litvinenko, and that President Vladimir Putin probably approved it.
The Russian government has denied any involvement in the Litvinenko killing or the attempted killing of Skripal, a former Russian agent who had served jail time in his homeland for spying for Britain before being freed in a spy swap.
Chemical weapons expert Richard Guthrie of the research project CBW Events, which records the use of chemical and biological weapons, said the highly public attack appeared to be "an expression of power" intended to send a message.