At least two Ukraine-based armed groups purporting to be made up of Russians opposed to the Kremlin launched an incursion across Russia's western border on Tuesday, according to their social media pages.
The Freedom of Russia Legion and the Siberian Battalion both announced on their Telegram pages that they had launched attacks into Russia from Ukraine.
"We will take our land from the regime centimeter by centimeter," the Freedom of Russia Legion said in its Telegram post.
Reuters could not independently verify the claims.
Russian officials could not be immediately reached for comment on the claims on Tuesday.
Ukraine says groups are acting independently
In the past, Russian officials have cast the groups as puppets of the Ukrainian military and US Central Intelligence Agency, which Moscow says is trying to foment chaos in Russia.
Andriy Yusov, a spokesperson for Ukraine's military intelligence, told Ukraine's 24 Channel the groups were conducting the operation on Russian territory independently of Ukraine.
Yusov said a third group, the Russian Volunteer Corps, was also participating in the operation.
The legion's post appeared to refer to the upcoming Russian election, which will take place this weekend.
"The people will vote for whom they want, not for whom they have to. Russians will live freely," the group said.
The Freedom of Russia legion and the Russian Volunteer Corps have previously claimed responsibility for other cross-border raids into Russia from Ukraine.