In its latest intelligence update, the defense chiefs say Wagner Group owner Yevgeny Prigozhin claimed in an online post that his engineering team was building a fortified defense line in Luhansk.
The Wagner Group is a private military company that acts as a Russian mercenary organization linked to the government, which has been denied by the Kremlin.
Satellite images from Ukraine showed a section of newly constructed anti-tank defenses and trench systems southeast of Kreminna in the Eastern Ukraine Oblast, the ministry tweeted.
The Ministry of Defense wrote: “If the plans are as extensive as Prigozhin claims, the work is probably aimed at integrating the Siversky Donetsk River into the defensive zone, partially following the 2015 Line of Control.
“The draft suggests that Russia is making a significant effort to prepare defenses in depth behind the current frontline that could deter any swift Ukrainian counteroffensive.”
Mr Prigozhin is a businessman with close ties to Vladimir Putin, who is also believed to be the head of Russia’s “troll farm”, the Internet Research Agency.
He is one of several oligarchs recently sanctioned by the West in response to the Russian invasion of Ukraine.
It comes after Russia launched a new wave of missile strikes on Ukrainian towns over the weekend as Mr Putin seeks to cut the country’s electricity, heating and water before winter.
Ukrenergo, the state-owned electricity provider, said Saturday’s attacks caused the most devastating damage to its systems in the west of the country to date. Yesterday, ten of Ukraine’s 24 regions and 1.5 million inhabitants suffered power cuts, including in the capital Kyiv.