Two U.K. citizens are hospitalized in critical condition after being exposed to the Novichok nerve agent — the same potentially lethal toxin that was used to poison former Russian spy Sergei Skripal and his daughter, Yulia, in March. The man and woman, both British and named in U.K. media reports as Charlie Rowley, 45, and Dawn Sturgess, 44, were found unconscious on Saturday at a house in the small town of Amesbury, just nine miles from Salisbury in southern England where the Skripals were attacked.

Police officers are seen standing guard outside a residential address in Amesbury, southern England, on July 5, 2018 where police reported a man and woman were found unconscious in circumstances that sparked a major incident after contact with what was later identified as the nerve agent Novichok.

They had been exposed to Novichok, a nerve agent developed in the Soviet Union in the 1970s, police said Thursday. The poisonings have raised barely settled tensions between the U.K. and Russia. British Security Minister Ben Wallace has called on Russia to provide more details about the Skripal attack so that authorities can “keep people safe,” while one senior Russian lawmaker called on the U.K. to ask Russian experts to take part in the latest investigation. As with the Skripal attack, Russia has denied any involvement in the latest incident. The Russian embassy in the Netherlands tweeted that Britain was “dumb” if it thinks Moscow would stage a nerve agent attack during the World Cup soccer tournament, which it is hosting through mid-July. A Russian lawmaker, Sergei Zheleznyak, said the latest incident looked like an attempt to spoil England soccer fans’ positive perception of the tournament, Reuters reported.

Investigation under way

The U.K. has not accused Russia of being behind the latest incident. The working theory is that the couple had a chance encounter with the nerve agent that might not have been properly disposed of after the Skripal attack. However, Metropolitan Police Assistant Commissioner Neil Basu could not confirm Wednesday whether the nerve agent that the British man and woman had come into contact with was the same as that used on the Skripals. Counterterrorism police have been brought in to investigate how the victims were exposed to the nerve agent, which can be up to eight times as lethal as VX, the nerve agent used to kill North Korean leader Kim Jong Un’s half-brother last year. Home Secretary Sajid Javid is scheduled to hold a meeting of the government's emergency Cobra committee Thursday to discuss developments. After weeks in a critical condition, the Skripals eventually recovered. Nonetheless, the Skripal attack caused deep damage to relations between the U.K. and Russia; the British government said Moscow was “highly likely” to have been behind the attack, given the high level of skill needed to produce Novichok.

Military personnel wearing protective suits remove a police car and other vehicles from a public car park as they continue investigations into the poisoning of Sergei Skripal on March 11, 2018 in Salisbury, England. Chris J Ratcliffe/Getty Images