Defense Secretary Gavin Williamson blamed Russian Federation for the "Novichok death" but police said they have no evidence to connect the Salisbury poisoning in March and the Sturgess poisoning Sunday.
British police rushed to solve a murder mystery on Monday (Jul 9) after a woman died following exposure to the nerve agent Novichok, four months after the same toxin was used against a former Russian spy in an attack that Britain blamed on Moscow.
"This is shocking and tragic news".
Tributes have flowed on social media, where Facebook friend Martin Bond described Sturgess as "a mother of a handsome daughter & a Good (sic) person".
"The staff here at Salisbury District Hospital worked tirelessly to save Dawn. They did everything they could".
They spent weeks in critical condition, but have both been discharged from Salisbury District Hospital, the same hospital where Sturgess died.
The Ministry of Defence is working with the police on the investigation and the clear-up effort, with 175 armed forces personnel involved. To date, of the five people allegedly exposed to it - the Skripals, Sturgess, Rowley and police Detective Sergeant Nick Bailey - only Dawn Sturgess has died while the other 4 have all recovered.
One line of inquiry suggests that after the Skripals were attacked by the nerve agent, the assailants disposed of vials, ampules or a mixing kit - or some other contaminated items - and that Rowley and Sturgess found the material and were accidentally exposed.
A post-mortem examination of Sturgess is due to take place and her family has been informed, police said.
They are also looking into where the couple came in contact with the poison, including searching the Queen Elizabeth gardens, a Salisbury homeless hostel where Sturgess, 44, lived and a red Ford Transit van 45-year-old Rowley traveled in hours before being rushed to the hospital.
Mr Basu said the priority was to determine how the pair came across an item contaminated with Novichok, a military-grade nerve agent produced in the Soviet Union during the Cold War.
Prime Minister Theresa May said that she was "appalled and shocked" by Ms Sturgess's death.
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. May also said her "thoughts and condolences" go to Sturgess' family and loved ones.
"Detectives are working as quickly and as diligently as possible to identify the source of the contamination, but this has not been established at this time", police said on Sunday.
In March, former double agent Sergei Skripal and his daughter Yulia fell critically ill after exposure to the nerve agent. Tests showed they were exposed after touching the nerve agent with their hands.
They had been exposed to an agent known as Novichok.
Mr Javid, who visited the site for around 25 minutes in total, met with Angus Macpherson, the Conservative police and crime commissioner for Wiltshire and Kier Pritchard, the Wiltshire police chief constable.
After the Skripal attack, Britain tossed out two dozen Russian diplomats suspected of being intelligence agents.