The top investigative body in Russia is looking at whether the SAS is “organising sabotage” in Ukraine.

The Investigative Committee – Moscow’s main federal investigating authority – said it would be following up a report from Russia’s RIA Novosti news agency.

RIA quoted a Russian security source as saying around 20 members of the SAS had been deployed in the western Lviv region, close to the border with Poland.

The Investigative Committee said it would look at whether – according to the report – the SAS had been sent in to “assist the Ukrainian special services in organising sabotage on the territory of Ukraine”.

The UK’s Ministry of Defence did not immediately comment.

A recent report in The Times, published on 15 April, said British special forces had begun training “local troops in Kyiv for the first time since the war with Russia began”.

The newspaper quoted Captain Yuriy Myronenko, who said military trainers had arrived to instruct new and returning military recruits to use British-supplied anti-tank missiles.

A week before the Russian invasion began, the British government said it had pulled all its troops out except those needed to protect its ambassador.

Prime Minister Boris Johnson has announced that the temporarily closed embassy will reopen next week.

Information on the SAS – Special Air service – is often highly classified. Its operations include direct action and covert reconnaissance.