Police called it a "significant and positive development" in the investigation
British police say they have found a bottle believed to have contained the nerve agent that has left one person dead and another seriously ill.
44-year-old Dawn Sturgess died on Sunday evening after being exposed to novichok.
Her partner, 45-year-old Charlie Rowley, became critically ill after also being exposed. He has since regained consciousness, and remains in a serious but stable condition.
Police investigating the incident say they found a 'small bottle' in Mr Rowley's house in Amesbury on Wednesday.
Scientists have now confirmed that the bottle contained novichok.
Detectives - who are treating the death of Ms Sturgess as murder - are now working to find out where the bottle came from and how it ended up in the house.
They are also looking to establish if the novichok is from the same batch used to attack former Russian spy Sergei Skripal and his daughter Julia in March.
Met Police Assistant Commissioner Neil Basu observed: "This is clearly a significant and positive development. However, we cannot guarantee that there isn’t any more of the substance left and cordons will remain in place for some considerable time.
"This is to allow thorough searches to continue as a precautionary measure for public safety and to assist the investigation team."
He added: "I also appreciate there is a lot of interest in this; however, we are not in a position to disclose any further details regarding the bottle at this stage."
The British government has blamed Russia for the attempted murder of Sergei and Yulia Skripal - claims Moscow has denied.
Both Ms Sturgess and Mr Rowley had been in Salisbury - the town where the Skripals were targeted - on the Saturday before they fell ill.
Police say any potential link between both novichok cases 'remains a main line of enquiry'.