Traces of a nerve agent used in the suspected attempted murder of a Russian former double agent have been found in a pub and a restaurant he visited, England's chief medical officer said Sunday.
Sally Davies said up to 500 people who had visited The Mill pub and the Zizzi restaurant in Salisbury, southwest England, should wash their clothes and belongings as a precaution.
Detectives are treating the March 4 attack on Sergei Skripal, 66, and his 33-year-old daughter Yulia as attempted murder.
The pair were found slumped on a bench in Salisbury. They remain in a critical but stable condition in hospital.
"There has been some trace contamination by the nerve agent in both The Mill pub and Zizzi restaurant in Salisbury," Davies said.
"I am confident this has not harmed the health of anyone who was in The Mill pub or Zizzi's."
People who were in the pub or restaurant last Sunday or Monday "should clean the clothes they wore and the possessions they handled while there," she said.
Pub and restaurant-goers were told to wash their clothing in the washing machine, while dry clean-only clothes should be put inside two tied plastic bags and safely stored while awaiting further advice.
Davies also gave detailed instructions for cleaning items such as mobile phones, handbags, jewellery and eyeglasses.
The risk to public health remained low and the advice was precautionary, Public Health England said.
"It is possible, but unlikely, that any of the substance which has come into contact with clothing or belongings could still be present in minute amounts," PHE said in a statement.
"Over time, repeated skin contact with contaminated items may pose a small risk to health."
Home Secretary Amber Rudd, Britain's interior minister, said Saturday that police were examining more than 200 pieces of evidence, had identified more than 240 witnesses, and were ploughing through security camera footage.
Around 180 troops, including chemical warfare experts, have been deployed in Salisbury after investigators requested expert assistance.
Military personnel wearing protective coveralls were seen setting up for an operation Sunday in a cordoned-off area behind a Salisbury police station.
Alastair Hay, an environmental toxicology professor at Leeds University, said the advice on cleaning clothes and possessions would provide an "extra guarantee of safety" for those who had visited the pub and restaurant.
"If no one has had physical symptoms suggestive of nerve agent contact by now it is unlikely that they are a risk," he said.
"Nerve agents vary in their rate of environmental breakdown. Sarin is one of those that degrades more rapidly whereas VX is more persistent... Nerve agents will form vapours and evaporate."
Skripal came to Britain in 2010 as part of a spy swap. He was a former colonel in Russia's military intelligence who was jailed in his country for betraying agents to Britain's MI6 secret service.
Britain's Foreign Secretary Boris Johnson has been pointing the finger at Moscow.
A public inquiry into the 2006 radiation poisoning death of Russian secret service defector Alexander Litvinenko concluded in 2016 that the killing in London had "probably" been carried out with the approval of President Vladimir Putin.
Litvinenko's widow Marina said it seemed that Britain was unable to protect those to whom it offered political asylum.
She revealed a 2016 letter from Theresa May, now Britain's prime minister, saying that "we will take every step to protect the UK and its people from such a crime ever being repeated".
"We can see nothing was done," she told Sky News television.
Nick Bailey, one of the first police officers on the scene after Skripal and his daughter fell ill, is in hospital but conscious.
"He's talking, he's engaging, still in a serious condition, but he is stable," said Kier Pritchard, chief constable of the local Wiltshire Police force.
"We wish Nick well, we look forward to him getting back on his feet."
Appealing for further information, he added: "This is a fast-paced, multi-faceted, complex investigation."