British police believe they have discovered the source of a nerve agent, which left one woman dead and a man critically ill.
A bottle with Novichok in it has been found at the address of surviving victim Charlie Rowley.
- Dawn Sturgess, UK woman poisoned by Novichok, dies
- Second Novichok poisoning likely from item missed in decontamination
- Poisoned Britons may have had chance encounter with Novichok
"This is clearly a significant and positive development, said Assistant Commissioner Neil Basu, head of UK counter terrorism policing.
"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."
Police say they are investigating whether the Novichok in the bottle is from the same batch that poisoned former Russian spy Sergei Skripal and his daughter Yulia Skripal.
The discovery was made a few days ago, but authorities only made the announcement on Saturday (NZ time), just three days before US President Donald Trump meets with Russian President Vladimir Putin.
It also comes as 12 Russian intelligence officers are indicted for hacking the Democratic Committee during the 2016 US Presidential election.