A nerve agent is suspected to have poisoned former Russian spy Sergei Skripal and his daughter, UK authorities said. Russia has denied any involvement the incident.
Police said a very rare nerve agent was suspected to be behind the poisoning of a former Russian spy and his daughter, which has prompted speculation of Moscow's involvement.
Police said on Wednesday that they were investigating the incident as an "attempted murder."
"This is being treated as a major incident involving attempted murder by administration of a nerve agent," Metropolitan Police assistant commissioner Mark Rowley said in a statement. "I can also confirm that we believe the two people originally who became unwell were targeted specifically."
Investigators said they would not be releasing additional information about the exact type of nerve agent they believe left Sergei Skripal, 66, and his 33-year-old daughter, Yulia, slumped over a bench outside a shopping center in the southwestern town of Salisbury on Sunday. They remain critically ill in the hospital. Sky News reported late on Wednesday that all three victims are in a coma. At least one police officer is also reportedly receiving treatment for exposure to the agent.
A British medical official said the agent poses a "low risk" to the general public.
"We need to keep a cool head and make sure we collect all the evidence we can," UK Home Secretary Amber Rudd said after chairing a government emergency committee meeting. "We need to make sure we respond not to rumor but to all the evidence that they collect. And then we need to decide what action to take."
The investigation is likely to take time, Rudd added.
She is expected to make a statement in parliament on Thursday.
Police are asking to speak to any witnesses who visited a pizza restaurant or pub where the two were seen on Sunday.
The area in and around Salisbury has been cordoned off.
Hundreds of counter-terrorism detectives are working "around the clock" on a timeline of the victims' movements and are reviewing "many hours" of CCTV footage, police said.
The Times newspaper reported that investigators are also looking into the deaths of Skripal's wife and son. His wife died of cancer in 2012 and his son of liver problems last year in St. Petersburg.
Speculation is rife that Russia attempted to assassinate the former military intelligence double agent.
Britain blamed Russia for the 2006 poisoning of former Russian spy and Kremlin critic Alexander Litvinenko.
British Foreign Secretary Boris Johnson suggested Sunday's incident had "echoes" of the Litvinenko assassination.
Moscow has denied any involvement and blamed anti-Russian bias from the media and politicians for trying to harm relations between the two countries.
"It's very hard not to assess this as provocative black PR designed to complicate relations between our two countries," Russian Foreign Ministry spokeswoman Maria Zakharova said Wednesday.
Skripal divulged the identities of Russian agents in Europe to Western intelligence and was imprisoned in 2006.
He was freed in 2010 as part of a spy swap that saw the United States hand over 10 members of a Russian spy cell in exchange for four Russians convicted of spying for Western intelligence agencies.
Royal World Cup boycott
Prime Minister Theresa May said the government could consider a boycott by British officials - but not include players - at the 2018 soccer World Cup in Russia this summer if Moscow is found to have been involved.
"Depending on what comes out in relation to the investigation [...} it might be appropriate for the government to look at whether ministers and other dignitaries should attend the World Cup in Russia," she said on Wednesday.
Several British media outlets said that Prince William would now not attend the World Cup in Russia, citing royal sources.
cw/sms (AFP, AP, Reuters)