British authorities vow to respond appropriately if foreign state involvement is found to be at play in the suspected murder attempt on former Russian spy Sergei Skripal and his daughter Yulia, who fell critically ill on March 4.

A police evidence tent is seen in a back garden on the road where former Russian intelligence agent Sergei Skripal lives, in Salisbury, Britain on March 11, 2018.
A police evidence tent is seen in a back garden on the road where former Russian intelligence agent Sergei Skripal lives, in Salisbury, Britain on March 11, 2018. (Reuters)

Traces of a nerve agent used in the suspected attempted murder of a Russian ex-spy and his daughter 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 the southwestern city of Salisbury at certain hours of March 4 and 5 needed to wash their clothes and belongings as a precaution.

Ex-spy Sergei Skripal and his daughter Yulia reportedly ate at Zizzi before falling critically ill on March 4.

"While there is no immediate health risk to anyone who may have been in either of these locations, 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 and therefore contaminate your skin," a statement by the Public Health England said. 

"Over time, repeated skin contact with contaminated items may pose a small risk to health."

The health agency added that any clothing should be washed in "an ordinary washing machine using your regular detergent at the temperature recommended for the clothing."

It also said to "wipe personal items such as phones, handbags and other electronic items with cleansing or baby wipes and dispose of the wipes in the bin."

Officials haven't said what type of nerve agent was used.

A large-scale police investigation is underway in Salisbury as forensics experts wearing protective gear search for clues. Among the sites they are searching are the Zizzi restaurant, which is closed to the public, and the gravesites where Skripal's wife and son are buried. Skripal's house has also been extensively searched for clues and traces of the nerve agent.

Wiltshire police planned to hold a news conference Sunday afternoon to release further details about the widening investigation.

UK to respond "appropriately" if foreign state involvement found

Senior government officials have vowed to respond robustly if the Russian government is found to be responsible.

British finance minister Philip Hammond said on Sunday that Britain's government would respond "appropriately" if a foreign state was found to be involved in the poisoning of a former Russian spy in England a week ago.

"This is a police investigation and it will be evidence-led and we must go where the evidence takes us," Hammond told BBC television.

"So we have to allow the police investigation to run its course. But if there were to be an involvement of a foreign state evidenced by this investigation, then obviously that would be very serious indeed and the government would respond appropriately," he said. 

Home Secretary Amber Rudd said also on Saturday evening it is still "too early" to determine who is to blame for the attack. 

Rudd said more than 250 counterterrorism officers are on the scene evaluating more than 240 pieces of evidence and interviewing about 200 witnesses.

They are backed by roughly 180 military personnel providing logistical support, including the removal of ambulances feared to possibly be contaminated by the nerve agent.

Police are looking for clues to what sickened Skripal, 66, a Russian ex-military intelligence specialist who in 2006 was convicted in Russia of spying for Britain, and his 33-year-old daughter, Yulia.

Skripal was imprisoned inside Russia until he was freed in a 2010 spy swap and settled in England. He had stayed out of the public eye since then.

The father and daughter were found unconscious March 4 on a bench in Salisbury. Skripal lived in the town, located 90 miles (140 kilometres) southwest of London.

Source: TRTWorld and agencies