London (CNN) Former Russian spy Sergei Skripal and his daughter were deliberately poisoned by a nerve agent, UK police say, significantly increasing the likelihood that a foreign state was behind the attack.

Mark Rowley, head of the counter-terrorism division of London's Metropolitan Police, told reporters that Sunday's incident was being treated as attempted murder. He revealed that one of the first police officers on the scene had fallen sick and was seriously ill in hospital.

The developments mean that the British government must confront the suspicion that elements linked to the Kremlin carried out a brazen attack with a deadly agent in the middle of a rural English city, two weeks before President Vladimir Putin seeks re-election for a new six-year term.

If a Moscow link were proved, it would plunge relations between the West and Russia into a new low, and would call into question the British government's ability to protect residents of the UK at home. Rowley said officers from Wiltshire police, the local force, were providing support to the sick officer and his families, but insisted there was no evidence of a wider threat to public health.

Skripal -- a former Russian military official convicted of spying for the UK -- and his daughter Yulia remain critically ill in hospital after being found unconscious on a shopping center bench. Police said they believe the pair were the specific targets of the attack.

Yulia Skripal (R) is thought to be one of the few members of her father's (L) immediate family still alive.

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