UK police have now launched a murder inquiry
Police in the UK have launched a murder inquiry after a woman who was exposed to the nerve agent novichok died in hospital.
Mother-of-three Dawn Sturgess, 44, died at Salisbury District Hospital on Sunday evening, Scotland Yard said.
She was admitted to hospital after falling ill at her partner's home in Amesbury, near Salisbury, last Saturday.
Her partner, Charlie Rowley, remains in hospital in a critical condition after the pair were exposed to novichok.
Police believe the pair were exposed to the substance through a contaminated item they came across accidentally.
Investigators think the item may have been left over from an attack targeting former Russian double agent Sergei Skripal and his daughter Yulia Skripal in March.
The pair were poisoned with the nerve agent just eight miles away in Salisbury, but managed to recover after spending months in hospital.
Britain has blamed Russia for the attack on the Skripals, but the Kremlin denies the allegation.
Detectives are still investigating the attempted murders of the Skripals and are looking into whether the separate incidents may be linked.
But officials said there is no evidence that the pair visited any of the sites in Salisbury which were decontaminated after the attempted murders of the Skripals.
Assistant Commissioner Neil Basu, the head of UK Counter Terrorism policing, said: "This is shocking and tragic news.
“Dawn leaves behind her family, including three children,” he said. “Our thoughts and prayers are with them at this extremely difficult time.”
"The 45-year-old man who fell ill with Dawn remains critically ill in hospital and our thoughts are with him and his family as well.
"This terrible news has only served to strengthen our resolve to identify and bring to justice the person or persons responsible for what I can only describe as an outrageous, reckless and barbaric act.
"Detectives will continue with their painstaking and meticulous work to gather all the available evidence so that we can understand how two citizens came to be exposed with such a deadly substance that tragically cost Dawn her life."
Police said nobody else has come to hospital with the same symptoms as the couple.
Prime Minister Theresa May said she was "appalled and shocked" by Ms Sturgess' death.
She added: "Police and security officials are working urgently to establish the facts of this incident, which is now being investigated as a murder.
"The government is committed to providing full support to the local community as it deals with this tragedy."
Professor Paul Cosford, from Public Health England, said the public is still being advised not to pick up "any strange items such as needles, syringes or unusual containers."
"The overall risk to the general public remains low," he added.
Ms Sturgess collapsed at about 10.15am on 30 June and was taken to hospital in an ambulance.
Mr Rowley was then taken to hospital at 3.30pm the same day, which is when police were informed.
Scientists at the UK's chemical laboratory Porton Down confirmed on Wednesday that the couple had been exposed to novichok.