British counterterrorism police say they believe they have found the source of the Novichok nerve agent that killed a woman in southwest England and made her partner critically ill.

Police said in a statement late on July 13 that a small bottle was found in the Amesbury residence of one of the victims, Charlie Rowley, and scientists confirmed that it contained Novichok, a military grade chemical weapon that was developed by the Soviet Union during the Cold War.

The police statement said more tests are being conducted to try to determine whether the Novichok in the bottle is from the "same batch" that poisoned former Russian spy Sergei Skripal and his daughter Yulia in March.

It said that a link to the Skripal poisonings in the nearby city of Salisbury remains a "main line of inquiry" for detectives investigating the Amesbury incident.

Rowley, 45, was the partner of Dawn Sturgess, 44, who died this month, just over a week after she was exposed to the Novichok in Amesbury, which is only a few kilometers from the Salisbury site where the Skripals were poisoned.

Rowley is now recovering in the same Salisbury hospital that treated and released the Skripals.

Neil Basu, the head of the U.K.'s counterterrorism police, said officers have spoken briefly to Rowley since he regained consciousness and want to pursue further conversations to "establish how he and Dawn came to be contaminated."

He said the discovery of the likely source of the couples' poisoning is "clearly a significant and positive development."

But he added that "we cannot guarantee that there isn’t any more of the substance left" in the areas where the bottle was found and the poisonings occurred.

While the risk of further poisonings remains "low," Basu said, "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 declined to give further details on the bottle as police investigate where it came from and how it came into Rowley's possession.

Before the bottle was found, police said they suspected the Amesbury victims had become contaminated with Novichok by handling a container, and they had no reason to think the two were targeted deliberately.

Police are now testing to see if the Novichok in the bottle came from the same batch that was applied to the front door of Skripal's house in Salisbury.

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 rejected the accusations and retaliated by expelling Western diplomats.

Britain has invited independent technical experts from the international chemical weapons watchdog to the United Kingdom early next week to test and independently confirm the identity of the nerve agent, the British Foreign Office said on July 13.

After a push by Britain and its allies in the wake of the Skripal incident, the Organization for the Prohibition of Chemical Weapons was recently given new authority not only to identify but to assign blame for incidents of chemical weapons use.

Russia and its ally Syria, which has been blamed for repeated use of chemical weapons in its seven-year civil war, strongly objected to giving the chemical watchdog such increased powers.

With reporting by AFP, dpa, Reuters, and AP

