British police have identified several Russians who they believe were behind the nerve agent attack on former double agent Sergei Skripal and his daughter, the Press Association reported on Thursday, citing a source close to the investigation.

Skripal, a former colonel in Russian military intelligence who betrayed dozens of agents to Britain's MI6 foreign spy service, and his daughter Yulia, were found unconscious on a public bench in the British city of Salisbury on March 4.

Britain blamed Russia for the poisonings and identified the poison as Novichok, a deadly group of nerve agents developed by the Soviet military in the 1970s and 1980s. Russia has repeatedly denied any involvement in the attack.