United Kingdom asks for information two years after Salisbury poisoning

British counterterrorism police have appealed for more information about a chemical weapons attack that nearly killed Russian-born double agent Sergei Skripal and his daughter two years ago.

It was the first official statement in 10 months on one of the biggest irritants in Britain's relations with Russia.

Britain blames to the attack on two Russian security service officers who allegedly entered Britain using false passports and poisoned Skripal and his daughter Yulia in the English city of Salisbury.

Russia denies the claims.

The Skripals spent days in a coma before recovering but local resident Dawn Sturgess died after picking up a discarded perfume bottle that was allegedly used to carry the poison.

Her partner, Charlie Rowley, spent weeks in hospital and a police officer also received a non-lethal dose of the Soviet-designed agent novichok.

The incident resulted in the largest ever expulsion of diplomats between Western powers and Russia.

UK counterterrorism police said late Sunday that the two Russians who entered Britain using the names Alexander Petrov and Ruslan Boshirov were still wanted.

But they said they could not piece together the full timeline of the attack.

"We continue to urge anyone who has information that they have not yet passed to police to do so," they said in a statement.

"In particular, we are keen to hear from anyone who may have seen the counterfeit Nina Ricci perfume box or bottle that was recovered from Charlie Rowley's address in July 2018."

Skripal and his daughter were found slumped unconscious on a park bench after eating at a local restaurant.

He was one of several suspected double agents involved in a spy swap that saw the United States return suspected spy Anna Chapman to Russia in 2010.

The New York Times said Skripal probably angered the Kremlin by continuing to provide information about Russian operations to Western security agencies after his return to Britain.

Russian officials say the chemical agent could have come from the British defence ministry's Porton Down lab near Salisbury.