Assistant Commissioner Neil Basu described her death as "shocking and tragic news" and said the force's thoughts are with the families of both victims.
A 44-year-old woman and a 45-year-old man, identified as British nationals Charlie Rowley and Dawn Sturgess, were found unconscious in their home in Amesbury on June 30. Picture: AAPCharlie Rowley remains in a critical condition.
Russia's Permanent Representative to the Organization for the Prohibition of Chemical Weapons Alexander Shulgin said Moscow would demand evidence from London supporting the words of British leaders about the possible involvement of Russia in the Amesbury poisoning, according to an interview published by Russian newspaper Izvestia on Monday.
Russian officials dismissed any claims that the Kremlin was responsible for the death of a British woman near Salisbury, in an incident that United Kingdom officials described as another case of the Novichok poisoning. They are among 21 people, including a police officer, who have been screened for Novichok poisoning since the latest incident came to light and given the all-clear.
British Prime Minister Theresa May said she was "appalled and shocked" by the death of Dawn Sturgess, one of two people who fell ill last weekend in Amesbury, near the town of Salisbury. Ms Sturgess has since died in hospital.
It came after former Russian spy Sergei Skripal and his daughter Yulia were targeted in the same city earlier this year.
Basu said the two "must have got a high dose" and police were seeking a "container" they are believed to have handled.
Mr Javid, who visited Wiltshire on Sunday, said Ms Sturgess's death "only strengthens our resolve to find out exactly what has happened".
"We don't know that Russian Federation has been mentioned or associated with this", President Vladimir Putin's spokesman Dmitry Peskov said.
Police are yet to recover that item but Public Health England said the risk to the public is low and warned against picking up "any odd items such as needles, syringes or unusual containers".
Police say the nerve agent that sickened Rowley and Sturgess was the same type that nearly killed the Skripals, but scientists haven't been able to tell whether it was from the same batch.
He and Ms Sturgess have been receiving care from the same team at Salisbury District Hospital which successfully treated the Skripals. This work will take time and the investigation must be allowed to proceed on the evidence and the facts alone.