A man and woman, now both in a coma at a hospital in southwest England, were poisoned by the nerve agent known as Novichok, the same type of Soviet-era chemical weapon used in an attack against a former Russian spy and his daughter four months ago, British counterterrorism investigators said late Wednesday.

Authorities said the latest two victims — identified by friends as British nationals Charlie Rowley, 45, and Dawn Sturgess, 44 — were found unconscious over the weekend at a residential property in Amesbury just a few miles from where a nerve agent was used in March to poison the former Russian double agent Sergei Skripal and his adult daughter, Yulia.

Witnesses told the British press that before Rowley and Sturgess succumbed they were frothing at the mouth, hallucinating and incoherent.

Testing to identify the poison in both cases was conducted by British scientists at a U.K. military research laboratory in nearby Porton Down, which specializes in work related to chemical weapons.

After a lengthy treatment, the Skripals were released from a hospital and continue to recover in an undisclosed location, protected by British authorities. Prime Minister Theresa May blamed Russia for the nerve agent assault against them.

The latest two victims were found in Amesbury, about eight miles north of Salisbury, where the Skripals were attacked.

Authorities said the cases may be related, but they did not say how. Did the latest victims somehow come into contact with nerve agent residue used to poison the Skripals — or was this an additional attack?

Scotland Yard Assistant Commissioner Neil Basu, a leader of the counterterrorism task force of 100 agents, said, “We are not in a position to say whether the nerve agent was from the same batch that the Skripals were exposed to. The possibility that these two investigations might be linked is clearly a line of inquiry for us.”

Basu did not say how or where the latest victims were exposed to the nerve agent but added, “At this stage, no one else has presented with the same symptoms linked to this incident. . . . The priority for the investigation team now is to establish how these two people have come into contact with this nerve agent.”

He said, “I would add that the complex investigation into the attempted murders of Yulia and Sergei remains ongoing, and detectives continue to sift through and assess all the available evidence and are following every possible lead to identify those responsible, for what remains a reckless and barbaric criminal act.”

British police declared a “major incident” early Wednesday — four days after the two victims were exposed. Local police initially suspected the two had consumed heroin or crack cocaine from a contaminated batch of drugs.

Sam Hobson, 29, a friend of Rowley and Sturgess’s, told the Daily Telegraph that the day before they fell ill, the three of them were in Salisbury visiting a number of sites in the town’s center, not far from where the Skripals were found.

A spokesman for the prime minister said the incident “is being treated with the utmost seriousness.”

Police cordoned off several sites in both Amesbury and Salisbury where they suspected the couple visited, including a church, a pharmacy and a park.