The highest examining body in Russia is espying in case the SAS is "organising sabotage" in Ukraine.
The Examining Committee which is Moscow's main federal investigating authority had said it would be following through on an information from Russia's RIA Novosti news agency.
RIA paraphrased a Russian safety expert as saying nearly 20 members of the SAS had been positioned in the western Lviv region, adjacent to the boundary with Poland.
The Examining Committee said it would espy in case as according to the information that the SAS had been dispatched to "assist the Ukrainian special services in organising sabotage on the territory of Ukraine".
The potential presence of British special forces emanating from a NATO country is substantial , bearing in mind that Moscow had cautioned the West not to barge in the way of what it calls its "special military operation" in Ukraine.
Other emerging issues:
• Ukrainian President Volodymyr Zelenskyy says he will meet US Secretary of State Antony Blinken in Kyiv on Sunday
• Boris Johnson speaks to Mr Zelenskyy about "new phase" of military aid including heavy weapons
• British intelligence suggests Russia has made no major gains in the last 24 hours
• Attempt to evacuate civilians from Mariupol fails
• Satellite images appear to reveal mass grave outside Mariupol
One week ago before the Russian irruption commenced, the British government said it had withdrawn its military forces out of Ukraine, with the exception of those required to safeguard its diplomat.
UK personnel had been grooming native military on how to use anti-tank weapons.
The impermanently shut Kyiv consulate will resume next week, Prime Minister Boris Johnson has declared.
Intelligence on the SAS - the Special Air Service - is often highly restricted. Its functioning include direct engagement and undercover counter espionage.
A Ministry of Defence pointperson said: "We do not comment on special forces."
A defence source said: "We don't comment on stories around special forces, especially ones that are being pushed out by the Russian news agencies, because inaccurate speculation can put people's lives at risk, which is why we neither confirm nor deny reports."
During a press briefing in Kyiv, President Zelenskyy said he has "no right to be afraid" of encountering the Russian President Vladimir Putin "because our people have shown they have no fear".
The conflict only be halted by those who began it, he informed journalists, adding that any "healthy person would choose the diplomatic way" over a military way to end the conflict.
He went on to say that overseas countries will finance diverse Ukrainian regions as part and parcel of a peace time reformation proposal.
Not less than five people were feared dead, including a three-month-old baby, following drone strikes in the southwestern port city on Saturday afternoon, Ukrainian officials said.
And additional 18 people were wounded, they added.
Projectiles are said to have pound a military facility and two residential buildings in the city.
Russian forces discharged more than six surface to air missiles, but most were dispirited by Ukrainian forces, the officials said.
The Russian defence ministry said it had used high sensitivity projectile to destroy a coordination work station where heaps of gunnery supplied by the US and European nations were being reserved.