A journalist for Russian-state media reportedly triggered a top-level security alert after he was observed filming outside a British military cyberwarfare headquarters.

Timur Siraziev was seen passing the 77th Brigade’s barracks in Hermitage, Berkshire, as he filmed a report for Russia’s Channel One alleging UK officials faked evidence to prove that Russia had committed war crimes in Syria, the Mail on Sunday said.

Siraziev is listed on the Russian embassy website as bureau chief for the television station and he is understood to have reported from Salisbury, Wiltshire, on the poisoning of Sergei Skripal and his daughter Yulia.

A senior army source said: “Timur Siraziev’s suspicious behaviour was monitored by the base’s security systems throughout.”

Siraziev told the Mail on Sunday he would not comment.

The 77th Brigade is understood to conduct cyber-attacks on terror networks, tackle propaganda online and engage in counter-piracy and counter-insurgency activities on the dark web.

According to the army website, it is a regular and reserve unit that aims to “challenge the difficulties of modern warfare using non-lethal engagement and legitimate non-military levers as a means to adapt behaviours of the opposing forces and adversaries”.

The Mail on Sunday provided an image of a leaked high-level alert issued last month after Siraziev was seen outside the brigade’s barracks, which shows the journalist’s press credentials and a car read: “Should this individual or vehicle attend any Army establishment security staff are NOT to allow admission, ensure two members of staff are present during any contact or conversation and contact local CIVPOL (civilian police) ASAP.”

The alert comes at a time of heightened political tensions between Britain and Russia following the poisoning of the Skripals earlier this year. Russia has repeatedly denied its agents were behind the attempted assassination.

The attack hospitalised a British police officer and three months later, two Wiltshire residents, Charlie Rowley and Dawn Sturgess, were exposed to novichok contained in the fake perfume bottle and Sturgess died.

Two Russian nationals were named and charged over poisoning of the Skripals. The investigative website Bellingcat identified the men as Alexander Mishkin, a doctor working for Russia’s GRU military spy agency, Col Anatoliy Chepiga, a special forces veteran.

In his reporting, Siraziev is understood to have described the case against Moscow as a hoax.

Days after the security alert, Channel One broadcast Siraziev’s eight-minute report on 77th Brigade. According to the Mail on Sunday, he told viewers: “In a forest 100km [60 miles] from London, a British army unit guards its secrets like a national treasure.

“There is a warning on the gates: police dogs. Two fences with barbed wire along the perimeter of the base. This is the 77th Brigade of the British army.”

The defence secretary, Gavin Williamson, said: “We take the security of our bases and personnel incredibly seriously. If a member of the public sees anyone acting suspiciously in or around a military base it should be reported to the police as a matter of urgency.”