British police believe, but can't yet prove, Novichok death connected to Skripal poisoning

British police said Monday they believe the latest victims of poisoning by a nerve agent must have handled the material's container and been subjected to a "high dose" of the lethal poison.

Dawn Sturgess died Sunday and her partner Charlie Rowley in critical condition in hospital

Police on Monday secure a point of interest in Salisbury, where counterterrorism officers are investigating after a woman and her partner were exposed to the nerve agent Novichok. Police said this is now a homicide investigation after Dawn Sturgess, 44, died Sunday. (Steve Parsons/PA via AP)

British police said Monday they believe the latest victims of poisoning by a nerve agent must have handled the material's container and been subjected to a "high dose" of the lethal poison.

Metropolitan Police Assistant Commissioner Neil Basu said the death of 44-year-old Dawn Sturgess on Sunday shows that she and partner Charlie Rowley, 45, were exposed to a large quantity of Novichok, a military-grade nerve agent produced in the Soviet Union during the Cold War.

Basu said the working theory is their exposure was linked to the earlier Novichok attack in March on ex-Russian spy Sergei Skripal and his daughter, Yulia, who have both survived despite extended hospitalizations.

But, Basu said, investigators are not yet able to make the forensic link between the incidents. He said the immediate police priority is to find any container that may be the source of the Novichok.

Britain has blamed Russia for the poisonings, but Moscow has strongly denied any involvement.

Speaking Monday in the House of Commons amid tensions over Brexit threatening to topple her government, Prime Minister Theresa May called it "an appalling crime."

"I'm sure the House will join me in sending our deepest condolences to the families and friends of Dawn Sturgess," she said.

"The police and security services are working urgently to establish the full facts in what is now a murder investigation."

'Russia has committed an attack on British soil,' says U.K. defence secretary 1:22

Interior Minister Sajid Javid said separately the "desperately sad news only strengthens our resolve to find out exactly what has happened."

Javid, who was chairing a meeting of the government's emergency committee on Monday, has said there were no plans at this stage for further sanctions against Russia.

Several people screened, cleared

Basu said no one else in the Amesbury and Salisbury region where the couple lived in southwestern England has shown any sign of Novichok poisoning, with over 20 people who had specifically screened for Novichok exposure cleared.

More than 100 police are working to try and search all areas where Sturgess and Rowley had been before they became ill nine days ago. The search is focused on their homes and a park in Salisbury.

Sturgess's survivors include three children. Rowley remains in critical condition in a Salisbury hospital.

Britain blames the Russian state for the attack on Sergei Skripal and 33-year-old Yulia — an allegation Moscow has repeatedly denied.

British authorities have not yet revealed what substance was used to threaten the lives of the former Russian spy and his daughter. (CBC)

A Kremlin spokesperson Monday expressed condolences over Sturgess's death.

Dmitry Peskov told reporters that Moscow "is deeply concerned" over the poisoning cases in Britain. Peskov added that such attacks present a danger not only inside the U.K., but also in Europe as a whole.

Peskov said that linking Russia to the poisoning would be "absurd."

Asked whether the death could cloud the upcoming U.S.-Russia summit in Helsinki next week, Peskov replied that the poisoning "has no relation" to the meeting. He said, "It's Britain's problem and the problem of how interested Britain is in a real investigation."

Moscow says London has declined its offers for a joint investigation into the poisonings.

With files from CBC News