Police reportedly identify key suspects in Skripal poisoning

British counter-terrorism police are reportedly trying to build a case against specific “persons of interest" who have returned to Russia in what could be a major breakthrough in the Salisbury poisoning of Sergei Skripal.

Searches of flight manifests in and out of the UK are believed to have yielded key names in the hunt for the would-be assassins, the Telegraph reported on Saturday.

Police have also drawn on extensive CCTV footage in the English market town, the newspaper said. The inquiry is expected to take "many" more months. Yulia Skripal has been released from the hospital while her father continues to receive medical care.

While UK authorities have blamed Russia for the March 4 nerve attack on the double agent and his daughter Yulia, Russia has denied any involvement.

Moscow has repeatedly stated its position through media conferences and mocking tweets on social media.

Decontamination work is due to start at nine locations in Salisbury where experts believe the nerve agent may still be present.

"We have to make an assumption that in certain circumstances there will be relatively high concentrations, probably in very, very specific locations, which could be at levels that could be toxic to individuals," Ian Boyd, chief scientific adviser of the Department for Environment, Food and Rural Affairs, reportedly told residents.

Britain accused Russia on Wednesday of breaking the two-decade international ban on chemical weapons at emergency talks in The Hague.

The accusations came as diplomats from the Organisation for the Prohibition of Chemical Weapons met behind closed-doors to discuss the crisis.

Britain's broadcasting watchdog, meanwhile, opened seven impartiality probes into Russia's RT news channel, noting "a significant increase" in programmes warranting investigation since last month's poisoning.