A couple in the town of Amesbury, England, was exposed Wednesday to the same nerve agent that sickened a former Russian spy and his daughter in a nearby town.
Investigators said the toxin tested positive for Novichok, the same material used to poison former Russian spook Sergei Skripal and his daughter last spring.
The British couple, in their 40s, is in critical condition at a hospital in Salisbury, where Skripal and his daughter were attacked in March, according to police in Wiltshire.
"It was initially believed that the two patients fell ill after using possibly heroin or crack cocaine from a contaminated batch of drugs. However, further testing is now ongoing to establish the substance which led to these patients becoming ill and we are keeping an open mind as to the circumstances surrounding this incident," police said in a statement.
Counterterrorism officers are now working with the police in Wiltshire after they declared a "major incident," the BBC reported, adding that the couple had been at a church family fun day before they were found unconscious.
Amesbury is about a 20-minute drive from Salisbury.
Both of the Skripals survived the March attack, which British authorities blamed on Russian authorities who Skripal had worked for before a conviction for selling secrets to the U.K. and a "spy swap" that sent him from prison to the English countryside.
Independent investigators at the Organization for the Prohibition of Chemical Weapons later confirmed that a nerve agent from the Novichok family was used.
Russian authorities have denied any involvement in the attack.
Russian President Vladimir Putin, a former KGB spy, plans to meet with President Donald Trump on July 16 in Helsinki, Finland.
