Traces of a nerve agent used to poison a former Russian spy and his daughter have been found in a pub and a restaurant they visited before falling critically ill, England’s chief medical officer says.
Sally Davies said on March 11 that up to 500 people who dined at the Zizzi restaurant or frequented the Mill pub in the city of Salisbury were told to wash their clothing and possessions as a precaution.
The investigation into the attempted murder of Sergei Skripal and his daughter Yulia is now in its seventh day.
Officials say the pair remain in a "critical but stable condition" at a Salisbury hospital after being exposed to a nerve agent, which they did not identify.
A police officer who fell ill attending the Skripals remains seriously ill but has been talking to his family.
The risk to the public remains low, officials say.
Earlier, British media reported that officials were talking to U.S. and European allies about coordinated retaliatory measures that could be implemented if it is determined Moscow is behind the poisoning.
“A wide range of options are being discussed,” The Times newspaper quoted a senior British official as saying on March 10.
The Times said retaliation could include stopping senior politicians or officials from attending the World Cup, scheduled for June 14 to July 15.
Other countries' teams that have qualified for the World Cup, such as Poland, Australia, and Japan, could also be asked to join any such moves, officials told the newspaper.
Officials said other measures could include bolstering NATO forces in Eastern Europe.
Some 4,000 troops have been deployed to NATO's eastern flank to reassure allies in the region concerned by Moscow's aggressive foreign-policy moves.
Following a government security meeting to discuss the nerve-agent attack, Home Secretary Amber Rudd said on March 10 that it was still "too early" to say who was behind the incident.
Foreign Secretary Boris Johnson has said that Britain might step up sanctions against Russia if it finds that Moscow was involved.
The Kremlin has denied involvement and asserted that anti-Russian hysteria is being whipped up by the British media.