British police say they have found a container they believe was the source of the nerve agent Novichok that killed one woman and left her partner in a serious condition in hospital.
- Police warn they can't be certain there are no more contaminated sites
- An inquest into Dawn Sturgess's death is set to open next Thursday
- A bottle which once contained Novichok was found in her partner's home
Dawn Sturgess, 44, died after coming in contact with the toxin. Her partner Charlie Rowley has regained consciousness but remains in a serious condition in Salisbury hospital.
"A small bottle was recovered during searches of Charlie Rowley's house in Amesbury," counter-terrorism police said in a statement.
"Scientists have now confirmed to us that the substance contained within the bottle is Novichok."
More tests were being carried out to try to establish whether it was from the same batch that contaminated former Russian spy Sergei Skripal and his daughter Yulia and inquiries were under way to establish where the bottle came from, the statement added.
Police say they will question Mr Rowley to try to determine why he had the bottle in his home.
Police unsure if there may be more Novichok in the area
Police warn they can't be certain there are no more contaminated sites.
"This is clearly a significant and positive development. However, we cannot guarantee that there isn't any more of the substance left," said Assistant Commissioner Neil Basu, head of UK counter-terrorism policing.
He said on Friday, local time, that cordons would remain in place in some locations to protect the public despite the apparent breakthrough in the case.
Assistant Commissioner Basu told local residents this week that Novichok could remain active for 50 years if it was kept in a sealed container.
The British Foreign Office said Britain had invited independent technical experts from the international chemical weapons watchdog to travel to the UK early next week to independently confirm the identity of the nerve agent.
The Organisation for the Prohibition of Chemical Weapons has the power to assign blame for chemical weapons use.
An inquest into Ms Sturgess's death is set to open in Salisbury next Thursday.
More than 100 police officers had been searching for the source of Mr Rowley and Ms Sturgess' exposure in Amesbury, where they lived, and Salisbury, where the Skripals were poisoned in March.
The Skripals survived and were released from the Salisbury hospital before Mr Rowley and Mr Sturgess were poisoned and taken there.
British authorities took the father and daughter to a secret, protected location.
Britain and its allies blamed Russia for the attack in March on the Skripals, prompting the biggest Western expulsion of Russian diplomats since the Cold War.
Moscow has rejected the accusations and has hit back by expelling Western diplomats.