British police say at least 21 people, including officers, have been treated after exposure to the nerve agent used to attack former Russian spy Sergei Skripal and his daughter near a U.K. shopping center.
Wiltshire Police Chief Kier Pritchard on March 8 said that a number of the victims "have been through the hospital treatment process...They are having blood tests, they're having treatment in terms of support and advice."
Three of the victims remained hospitalized, a police official said, identifying them as Skripal, his daughter Yulia, and police Sergeant Nick Bailey, who responded to the incident.
Skripal, 66, and his 33-year-old daughter were listed in "critical" condition four days after they were found unconscious on a bench outside a shopping mall in Salisbury after stopping at a restaurant and pub in the southern English city.
Bailey, who was among the first on the scene, was awake and talking, but his condition remains serious, Home Secretary Amber Rudd said.
"He’s not in intensive care, but it is a serious situation," she said, declining to give any further details on the exact nature of the nerve agent used.
Officials did not immediately explain how the others might have been exposed to the substance.
Britain's chief medical officer, Sally Davies, said the general public was not necessarily at high risk, but experts said nerve agents are dangerous and extremely volatile.
A spokesman for British Prime Minister Theresa May said the poisoning was an "appalling and reckless crime.”
Rudd, meanwhile, told parliament that the use of a nerve agent on British soil was "a brazen and reckless act" but that Britons must avoid speculating on who was behind it.
"This was attempted murder in the most cruel and public way," said Rudd, Britain's top police official. "But if we are to be rigorous in this investigation, we must avoid speculation and allow the police to carry on their investigation."
Rudd said British authorities "will respond in a robust and appropriate manner once we ascertain who was responsible."
"We are committed to do all we can to bring the perpetrators to justice, whoever they are and wherever they may be," she said.
A police officer who was among the first on the scene was also harmed but is now awake and talking, Rudd said earlier on March 8 on British radio, adding that his condition remains serious.
"He’s not in intensive care, but it is a serious situation,” she said, but declined to give any further details on the exact nature of the nerve agent used.
Skripal, a retired Russian military intelligence colonel, was one of four prisoners released by Moscow in exchange for 10 U.S. spies in 2010, as part of a swap.
Counterterrorism officers are working to find the origin and type of the nerve agent used in the attack.
ALSO READ: Toxicologist: Lab With 'Military Capability' Likely Made Poison Used On Russian Ex-Spy
The statements from the prime minister and home secretary came after Mark Rowley, head of Counterterrorism Policing, first announced on March 7 that the illnesses were being treated "as a major incident involving attempted murder, by administration of a nerve agent."
Rowley's statement ended days of uncertainty about whether the incident was an attack or an accident.
Nerve agents such as sarin are highly toxic chemicals that disrupt the nervous system and shut down bodily functions.
The substance used on March 4 was likely to be rarer than sarin or VX nerve agents, the BBC reported on March 8, citing an unnamed source.
Skripal was arrested in Moscow in December 2004 and convicted by a Moscow military court in August 2006 of "high treason in the form of espionage."
He was found guilty of passing the identities of Russian intelligence agents working undercover in Europe to Britain's Secret Intelligence Service, or MI6, in return for $100,000.
Russia’s Federal Security Service (FSB) alleged he had begun working for MI6 while serving in the army in the 1990s.
The incident in Salisbury has drawn comparisons with the 2006 death of former Russian security agent Aleksandr Litvinenko in London.
A British inquiry has concluded that the Russian government was behind Litvinenko's death and that President Vladimir Putin "probably approved" the killing. Russia has denied any involvement.
Foreign Secretary Boris Johnson has warned that any involvement of a foreign government in the incident in Salisbury would not go "unpunished."
Johnson told Parliament on March 6 that Britain might step up sanctions against Russia if it finds that Moscow was involved. He also suggested that Britain could reconsider its participation in the soccer World Cup in Russia this summer.
The Russian Foreign Ministry has accused British politicians and journalists of using the case to drive "anti-Russian" sentiment and disrupt relations between London and Moscow.
Relatives of Skripal were quoted in the British media as saying that some of his family members died in recent years under mysterious circumstances.
They told the BBC Russian Service that the ex-spy believed that "Russian special services might come after him at any time."
Skripal's son Sergei, 44, died on a visit to Russia last year of an unknown illness, The Times newspaper reported, while The Guardian reported that Skripal's wife died from cancer shortly after her arrival in Britain in 2012.
The Times reported that Yulia Skripal lived in Britain in 2010 after her father was released in a spy swap with Russia, but she later moved back to Moscow and was working for PepsiCo Russia. She returned to Britain to visit her father last week, it said.