British officials say a man and woman have been critically injured by the same Russian nerve agent used against a former spy and his daughter.
Investigators are seeking clues after the two were exposed to the Soviet military-grade substance "Novichok."
The couple fell critically ill a few miles from where a former Russian intelligence officer, Sergei Skripal, and his daughter, Yulia, were poisoned with Novichok in March.
Britain blamed Russia for the March attack, but Moscow officials denied any involvement.
Regarding this latest incident, President Vladimir Putin's spokesman, Dmitry Peskov, told reporters that Russia has "categorically denied and continues to categorically deny the possibility of any kind of involvement."
"Two drug addicts were poisoned with serious drugs and the British intelligence services and the British leadership are now trying to interpret this incident as a continuation of the Skripal poisoning," said Peskov.
Meanwhile, UK police say they are investigating whether there is a link between the two cases.
"It's very difficult to say how it would be linked unless you know something about the people who've become the casualties," Major General Chip Chapman, former head of counter-terrorism for the Ministry of Defence, said.
"What they'll be doing is looking into their background to see if there is any reason that they would be linked to the Skripals at all," he explained. "But that would be highly unlikely it seems to me."
Security Minister Ben Wallace told BBC News Thursday that the couple is likely just a victim of the consequences of the earlier attack and that they were not directly targeted.
This latest case of poisoning has raised public health concerns in the Salisbury area, where a massive decontamination effort took place after the Skripals were poisoned.
"Although Novichoks are quite persistent, they maintain their toxicity for months, whereas older nerve agents only last for hours and possibly days," explained Hamish de Bretton-Gordon, a chemical weapons expert.
The man and woman are currently critically ill in England's Salisbury District Hospital, where the Skripals were previously treated.
Meanwhile, Russian lawmaker Sergei Zheleznyak has described the incident as part of British efforts to tarnish the Russia-hosted World Cup and fuel tensions ahead of a planned US-Russia summit.
"This is happening during a quite strong, positive, emotional wave from British fans who have come to Russia to support their team during the World Cup," Zheleznyak said. "This, of course, fully dissonates with what the British authorities and the British media are saying about Russia. That is why they needed a new precedent to try to smear Russia with something nasty."