Vladimir Putin has deployed a special unit of guards to Moscow amid rising fears of a coup, Ukrainian intelligence sources have claimed.
Intelligence officials said the elite ODON unit of the Russian National Guard is bolstering security around the Russian capital and that all military units are on "high alert".
The briefing came hours after the Kerch bridge linking Russia to Russian-annexed Crimea was partially destroyed in a suspected Ukranian attack.
Ukraine has not claimed official responsibility for the strike, with some officials suggesting that it was a result of Russian infighting.
ODON troops - formally named the Separate Operational Purpose Division - are a rapid deployment internal security division of the Internal Troops of the Ministry of Internal Affairs.
Ukrainian intelligence sources claim the 18,000-strong military unit commanded by Major General Nikolai Kuznetsov have started setting up blockades in the capital and arresting soldiers deemed a threat to Russian security, reports The Sun.
It comes as Putin is planning to hold an operational meeting of his Security Council on Monday two days after the Kerch bridge explosion, which he has called an "act of terrorism".
Speaking at a meeting alongside the head of the Investigative Committee of Russia, Alexander Bastrykin, Putin also formally accused Ukraine of being behind the attack.
"There is no doubt, this is an act of terrorism aimed at destroying Russia's critical civilian infrastructure," he said, according to the BBC. "Its authors, perpetrators and beneficiaries are the security services of Ukraine."
Mr Bastrykin said that the truck they say blew up on the bridge had travelled through Bulgaria, Georgia, Armenia, North Ossetia and Krasnodar Territory. He has ordered an official investigation into the incident.
One adviser to Ukraine's President Volodymyr Zelensky, Mykhailo Podolyak, did not claim Kyiv was directly responsible.
He said that there is "only one terrorist state here" and that the "whole world knows who it is".
"Does Putin accuse Ukraine of terrorism? It looks too cynical even for Russia," he added.
Some road traffic has resumed along the bridge following a speedy repair job from Russian engineers. The section of railway that caught on fire has also been mended.
On Sunday, a flurry of missile strikes on the southern Ukrainian city of Zaporizhzhia killed 13 people including one child, according to Kyrylo Tymoshenko, deputy head of the Office of the President of Ukraine.
Oleksandr Starukh, head of Zaporizhzhia regional military administration, said that at least 89 civilians were injured in the strikes, including 11 children.
