LONDON - Security agents in Britain are working around the clock to discover how and why a British couple in Wiltshire were exposed to the nerve agent Novichok, Home Secretary Sajid Javid said Thursday.

Briefing MPs in the House of Commons after chairing a meeting of Britain's top security committee, Cobra, Javid said it was not known whether the latest incident was linked to the Novichok attack in March in the city of Salisbury on Russian agent Sergei Skripal and his daughter Yulia.

The latest victims, Charlie Rowley, 45, and Dawn Sturgess, 44, fell ill at a house in Amesbury in Wiltshire on Saturday and remain in a critical condition in Salisbury District Hospital.

"There is no evidence that the pair recently visited any of the sites that were part of the original clean-up operation," said Javid, saying the assumption is that they came into contact with the Novichok somewhere else.

"The authorities are working around the clock to discover what happened," he said, adding that all the sites that were decontaminated after the Skripal poisoning are safe.

"People will want to know if this incident is linked to the Skripal poisoning. That is clearly the main line of inquiry."

Javid said he was aware some residents in Wiltshire were feeling anxious, but the advice from Public Health England was that the risk to the public is low and there is no significant risk to the general public.

Media reports said Rowley and Sturgess had attended a family fun day at a church in Amesbury hours before they were found in a collapsed state.

The church was Thursday one of six new areas cordoned off in the area to enable intensive checks to be carried out by experts.