The independent Bellingcat research organization says it has reviewed Russian documents, which indicate that the two men suspected in the poisoning of British spy Sergei Skripal have no records in the Russian resident database prior to 2009, a sign they may be working as operatives for the government.
Bellingcat said on September 14 that a joint investigation with The Insider Russia "directly contradicts" claims by the Kremlin that Ruslan Boshirov and Aleksandr Petrov are civilians who traveled to Salisbury, England, where the poisoning took place, for a tourist getaway.
The investigation, Bellingcat said, showed that, while the two men were registered in the central Russian resident database and were issued internal passports under their names in 2009, no records exist for the two prior to 2009.
"This suggests the two names were likely cover identities for operatives of one of the Russian security services," Bellingcat said.
"Crucially, at least one man’s passport files contain various "top-secret" markings, which, according to at least two sources consulted by Bellingcat, are typically reserved for members of secret services or top state operatives," it added.
Britain has charged the two men with attempting to murder Skripal and his daughter Yulia.
British authorities accuse them of spraying a military-grade nerve agent, Novichok, on Skripal’s front door in Salisbury in March.
Earlier on September 14 the Kremlin said it would study any British request to question the two but spokesman Dmitry Peskov said no such a request had been received so far.
He also reiterated Kremlin denials of any Russian state involvement in the poisoning.
Peskov’s comments come a day after the two men appeared in an interview on Kremlin-funded RT television station to proclaim their innocence.
The two denied they were agents of the military intelligence service widely known as the GRU and said they were merely tourists in the city southwest of London.
"Our friends had been suggesting for quite a long time that we visit this wonderful city," Petrov said in the interview.
"They have a famous cathedral there," Boshirov said, adding: "It is famous for its 123-meter spire."
James Slack, spokesman for British Prime Minister Theresa May, derided their claims as "lies and blatant fabrications.
"More importantly, they are deeply offensive to the victims and loved ones of this horrific attack," he said.
British officials have accused the suspects of smuggling Novichok into Britain in a fake perfume bottle and smearing some of it on the front door of Skripal's home in Salisbury, where the former intelligence officer settled after being sent to the West in a Cold War-style spy swap in 2010.
The attack left Skripal, 67, and his daughter Yulia, 34, in critical condition, but both have recovered after weeks in the hospital.
The men interviewed by RT denied carrying the fake women's perfume bottle with them.
"Isn't it silly for decent lads to have women's perfume?" one of the two men was quoted as saying by the Kremlin-funded RT.
"The customs are checking everything.They would have questions as to why men have women's perfume in their luggage. We didn't have it."
They also said they stayed less than one hour in Salisbury due to poor weather.
"We went there to see Stonehenge, Old Sarum, but we couldn't do it because there was muddy slush everywhere," one of the two men said, referring to local landmarks.
In a statement, the British government said the interview reflected more "obfuscation and lies" by Moscow.
"The government is clear these men are officers of the Russian military intelligence service -- the GRU -- who used a devastatingly toxic, illegal chemical weapon on the streets of our country," it said.
"We have repeatedly asked Russia to account for what happened in Salisbury in March," the statement also said. "Today -- just as we have seen throughout -- they have responded with obfuscation and lies."
The RT interview was aired a day after Russian President Vladimir Putin said his country had identified the men Britain suspects of poisoning Skripal and his daughter, but claimed they were civilians.
"They are civilians, of course," Putin said on September 12.