British citizen Dawn Sturgess died on Sunday in a hospital after coming in contact with a deadly Russian-linked Novichok nerve agent in Amesbury, Wiltshire, the Metropolitan Police announced.

Sturgess, 44, from Durrington, and Charlie Rowley, 45, were exposed to the deadly nerve agent. He remains critically ill in the hospital.

Prime Minister Theresa May said: “I am appalled and shocked by the death of Dawn Sturgess, and my thoughts and condolences go to her family and loved ones. Police and security officials are working urgently to establish the facts of this incident, which is now being investigated as a murder.”

Police detectives from the Counter Terrorism Policing Network are leading the investigation alongside the Wiltshire police.