Vladimir Putin has said it's “not possible” that Sergei and Yulia Skripal were poisoned in Salisbury by a military nerve agent and raised doubts about British allegations that Russia attacked them.

“I'm not an expert in military grade toxic agents, but as far as I can picture, if a military grade toxic agent is used, then the victims of this attack die on the spot, almost immediately,” Mr Putin said, speaking with news editors at the St Petersburg economic forum. “This didn't happen, Skripal and his daughter are alive and have been released from the hospital. And his daughter looks well enough, everyone is alive and healthy.”

“It's not possible to say this was a military grade nerve agent,” Mr Putin continued. “And if that's the case, then it casts into doubt everything that was said by the British side from the start.”

The international chemical weapons watchdog said Novichok, a sophisticated nerve agent developed in the Soviet Union, was used to poison the Skripals. The UK government has said it's "highly likely" the Kremlin was behind the attack, despite Russian denials.

On Wednesday, Yulia Skripal said she and her father had undergone a “slow and extremely painful” recovery after they were found slumped on a Salisbury park bench. She again declined the services of the Russian embassy in London, which has repeatedly attempted to see her.