"This is shocking and tragic news", Neil Basu, of the UK's counterterrorism agency, said. She and her partner Charlie Rowley were hospitalized after both fell seriously ill in what was initially believed to be a drug-related incident.
The UK's top counter-terrorism officer says police are unable to confirm whether the Novichok nerve agent to which a couple was exposed in Amesbury was from the same batch used to poison the Skripals in Salisbury last March.
The attack on the Skripals worsened the already tense relations between Russia and the West, prompting the expulsion of Russian diplomats and embassy workers from several countries and retaliatory expulsions by Moscow.
The Kremlin has said that it was sorry to hear about the death of Ms Sturgess, but said that any suggestion that Russian Federation was involved would be "quite absurd".
It is unknown if the incident is connected to the major police investigation in the the Novichok poisoning crisis.
The British couple, Sturgess and Rowley, were found on May 30 unconscious at a house in Amesbury, Wiltshire - about 10 miles from where Skipal and his daughter were poisoned.
Sturgess, 44, died in the hospital Sunday evening. The government has blamed Russian Federation for the March poisoning. Three men who also travelled in it show no signs of having been exposed to novichok.
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It came after former Russian spy Sergei Skripal and his daughter Yulia were targeted in the same city earlier this year.
After Sturgess' death on Sunday, Britain's interior minister, Sajid Javid, said the "desperately sad news only strengthens our resolve to find out exactly what has happened".
Detectives have also pieced together a detailed timeline of Ms Sturgess and Mr Rowley's movements prior to falling ill.
Police in HAZMAT suits as they investigate the poisoning of two people in Salisbury.
"We have told our British colleagues that they are playing with fire and they will be sorry", he said. Mr Rowley was then taken to hospital at 3.30pm the same day, which is when police were informed.
Professor Paul Cosford, from Public Health England, said the public is still being advised not to pick up "any odd items such as needles, syringes or unusual containers".
Dr Christine Blanshard, medical director at Salisbury District Hospital, expressed her condolences to Ms Sturgess' family and said her staff "did everything they could". This work will take time and the investigation must be allowed to proceed on the evidence and the facts alone.
This has been identified as the same type of nerve agent that contaminated both Yulia and Sergei Skripal.