British media says traces of the nerve agent used to attack a Russian ex-spy and his daughter have been found in Salisbury where the two were poisoned.

BBC and Sky News said today that traces have been detected. BBC said its sources say traces were found at the Zizzi restaurant where Sergei Skripal and his daughter Yulia reportedly ate before falling critically ill. Sky says traces were found in several locations.

UK officials haven't publicly confirmed that any trace of the nerve agent has been found and say the risk to the public remains low. 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.