Sergei Skripal
Sergei Skripal

A former Russian spy is in critical condition after being exposed to an unknown substance in the English town of Salisbury.

British media have identified the man as Sergei Skripal, who was given refuge in Britain after a spy swap between the United States and Russia in 2010.

British broadcaster BBC said Skripal, 66, and a woman in her 30s were found unconscious on a bench at a shopping center in Salisbury on Sunday afternoon.

Wiltshire Police, which is responsible for the Salisbury area, only identified the two by their approximate ages and said "the pair, who we believe are known to each other, did not have any visible injuries and were taken to Salisbury District Hospital."

Craig Holden, temporary Assistant Chief Constable of the Wiltshire Police, said  "They are currently being treated for suspected exposure to an unknown substance. Both are currently in a critical condition in intensive care."

He said the police force "received a call from a member of the public who was concerned for the welfare of two people."

Holden said because the investigation is in its very early stages, "we are unable to ascertain whether or not a crime has taken place."

Skripal was convicted in Russia of spying for Britain's MI6 intelligence agency and was sentenced in 2006 on charges of espionage. He was pardoned in 2010 as part of a U.S.-Russian spy swap.

Relations between Britain and Russia have been strained since former KGB-agent Alexander Litvinenko was poisoned in London in 2006. A British inquiry concluded Litvinenko was probably killed on the orders of Russian President Vladimir Putin.