LONDON -- Police believe they have identified suspects who carried out the Novichok attack on a former Russian double agent and his daughter in the English city of Salisbury, the Press Association reported Thursday. "Investigators believe they have identified the suspected perpetrators of the Novichok attack through CCTV and have cross-checked this with records of people who entered the country around that time," a source with knowledge of the investigation told PA, the British domestic news agency.

"They (investigators) are sure they (suspects) are Russian," the source added.

Scotland Yard police headquarters refused to comment on the report when contacted by AFP.

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Ex-Russian spy Sergei Skripal and his daughter Yulia collapsed in the city of Salisbury on March 4 after being exposed to the nerve agent Novichok. Both have since recovered.

Britain blamed Russia for the poisoning of Skripal, a former military intelligence colonel who was jailed for betraying Russian agents to Britain's MI6 foreign intelligence service.

He left Russia for England in a 2010 spy swap.

Russia has strongly denied involvement in the Skripal attack, sparking a diplomatic row that has led to tit-for-tat diplomatic expulsions between Britain and its allies and Russia.

Two Britons fell ill in June after being exposed to Novichok in the same region of southwest England. Experts are seeking to establish whether the toxin was from the same batch used against the Skripals.

Charlie Rowley, 45, and his 44-year-old partner Dawn Sturgess, collapsed at his house in Amesbury, a town close to Salisbury, within hours of each other on June 30.

Sturgess died on July 8, while Rowley has regained consciousness and is in stable condition.

PA said investigators believe Sturgess was exposed to at least 10 times the amount of nerve agent as the Skripals came into contact with.

Rowley's brother Matthew told BBC news that the 45-year-old had told him the Novichok was contained in a perfume bottle.

Police have said it was detected in a "small bottle".

An inquest into the death of Sturgess was to open on Thursday at Wiltshire and Swindon Coroner's Court in Salisbury.

In English law, inquests are held to examine violent, unnatural or unexplained deaths. They set out to determine the place and time of death as well as how the deceased came by their death, but do not apportion blame.

The inquest will be formally opened but then adjourned to a later date.

The Organisation for the Prohibition of Chemical Weapons said its inspectors had collected samples in the Amesbury case and returned to the organisation's headquarters in The Hague on Wednesday to begin analysing them.

The organisation said in a statement that it had reveived a request from Britain on Friday to provide technical assistance.

They deployed a team to "independently determine the nature of the substance" alleged to have resulted in the death of Sturgess and the poisoning of Rowley.

"The OPCW team collected samples. The samples will be sent to two OPCW designated laboratories and once the results of the analysis are received, the report will be submitted to the United Kingdom," it said.