File photo: Dawn Sturgess (Photo courtesy: Twitter.com)
The woman who was exposed to the nerve agent Novichok in Wiltshire in southern England has died in hospital, British police said.
Dawn Sturgess, 44, and her partner Charlie Rowley were found unconscious last week, a few kilometres from the scene of a nerve agent attack on a former Russian spy and his daughter in March.
Prime Minister Theresa May said she was "appalled and shocked" by the death of Dawn Sturgess.
"Police and security officials are working urgently to establish the facts of this incident, which is now being investigated as a murder," she said.
She offered her condolences to the relatives and loved ones of Sturgess, 44, who had three children. She became ill alongside a man named locally as Charlie Rowley, 45.
They were believed to have become exposed to Novichok by handling a container, and a link to the Salisbury attack in March is a main line of investigation.
That incident left former Russian spy Sergei Skripal and his daughter Yulia, who was visiting from Russia, in a critical condition although they later recovered.
Britain and its allies blamed Moscow for trying to kill the pair, prompting angry denials that led to an international diplomatic crisis.
More than 100 detectives have been working alongside local officers to locate a small vial or other container thought to have held the nerve agent that sickened the two.
Officials said the search and clean-up operation would take weeks or even months.
Counter-terrorism police were also studying roughly 1,300 hours of CCTV footage in hopes of finding clues about the couple's activities in the hours before they became violently ill.
(With inputs from Agencies)