Christine Blanshard, medical director at Salisbury District Hospital, where Sturgess and Rowley were being treated and where the Skripals were hospitalised, told The Daily Telegraph newspaper that staff had "worked tirelessly to save Dawn".
The nerve agent was developed by the Soviet Miliary during the Cold War.
A woman who was poisoned by a military-grade nerve agent in southwest England died Sunday, eight days after police think she touched a contaminated item that has not been found.
Dawn Sturgess, 44, succumbed to her injuries in a hospital in Salisbury, according to the Metropolitan Police in the United Kingdom. Still, more than 20 other countries have expelled Russian diplomats in a show of support for the UK.
"This latest horrendous turn of events 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".More news: Timehop’s data breach compromised 21 million accounts
British police said they believe Sturgess and her partner, Charlie Rowley, must have handled a container of the substance and been exposed to a "high dose".
Britain blames the Russian state for the attack on Sergei Skripal and his 33-year-old daughter - an allegation Moscow strongly denies.
Members of the media stand outside a police cordon stopping people seeing a property shielded from view, around to the left out the picture, that police have been guarding in Amesbury, England, Thursday, July 5, 2018.
The Britons were initially thought to have taken an overdose of heroin or crack cocaine.
Britain has notified the global chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons (OPCW).More news: Ohio Abuse Scandal Spurs Blaming of the "Deep State"
Confirmation from authorities Wednesday that two British citizens were exposed to Novichok shook residents around Salisbury, who thought a months-long cleanup had removed any threat from the powerful nerve agent. It came as Scotland Yard said it "cannot offer any guarantees" that others won't be poisoned and revealed a red van travelled in by Mr Rowley on the day he fell ill has been sent to Porton Down for testing.
So far, the government has been cautious about going full-throttle in its attack on Russian Federation. He remains in a critical condition. After reviving from comas, both were released from the hospital to an undisclosed location. Her father Stephen, 65, said his family was "devastated".
Alastair Hay, a professor of environmental toxicology at Leeds University, said the hospital probably now had more experience than anywhere else in the world with Novichok cases, but there were limits to what doctors could do.
"The fact that a nerve agent was used to do this was shocking", she said.
The investigation is being led by detectives from Britain's Counter Terrorism Policing Network and around 100 detectives are working round the clock alongside colleagues from Wiltshire police.More news: J.B. Smoove Joins Spider-Man: Far From Home Cast
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