AMESBURY, England — For the second time in four months, two people lie critically ill in England’s Salisbury District Hospital after being exposed to a military-grade nerve agent developed in the Soviet Union, British police confirmed late Wednesday.
The country’s chief counterterrorism police officer said tests at Britain’s defense laboratory had confirmed what many residents feared — a man and woman in their 40s had been poisoned with the same toxin that almost killed a former Russian spy and his daughter.
‘‘We can confirm that the man and woman have been exposed to the nerve agent Novichok, which has been identified as the same nerve agent that contaminated both Yulia and Sergei Skripal,’’ said Assistant Commissioner Neil Basu of London’s Metropolitan Police.
Basu said it was not clear whether there was a link between the two cases, and whether the nerve agent came from the same batch that left the Skripals fighting for their lives.
Wiltshire Police declared the case a ‘‘major incident’’ Wednesday, four days after the man and woman were found collapsed at a residential building in Amesbury, 8 miles from Salisbury, where the Skripals were poisoned. A major incident designation allows British authorities to mobilize more than one emergency agency.
Police said officers were initially called Saturday morning about a collapsed woman, then were summoned back in the evening after a man fell ill at the same property. Police at first thought the couple, identified by friends as 44-year-old Dawn Sturgess and Charlie Rowley, 45, had taken a contaminated batch of heroin or crack.
London’s Metropolitan Police said that ‘‘given the recent events in Salisbury,’’ counterterrorism officers were working with local police on the investigation.
Prime Minister Theresa May’s office said she was being kept updated on the case, ‘‘which understandably is being treated with the utmost seriousness.’’