The border post of Grajvoron and the nearby village of Kozinka have been "liberated", and the armed groups say they are heading towards the town of Grajvoron with just over 6,000 inhabitants.
"The purpose is to create a demilitarized zone on the border to prevent Russian artillery shelling of Ukraine," the group, which is fighting on Ukraine's side, said in a message to SVT Nyheter.
Kremlin: Ukrainian saboteurs
The Russian Ministry of Defense confirms the attack, and Kremlin spokesman Dmitry Peskov claims that they are Ukrainian saboteurs, and that it is an attempt by Ukraine to shift the focus from the loss of Bachmut.
The Ukrainian military says it is the two Russian opposition groups and not the Ukrainian army that have entered Russia.
"The guerrilla groups are made up of Russian citizens," Mykhaylo Podolyak, an adviser to Ukraine's president, wrote on Twitter.
Security forces to stop the attack
The governor of Russia's Belgorod Vyacheslav Gladkov says Russian soldiers and security forces have now been deployed in the area to stop the attack. Gladkov rejects reports of an imminent evacuation of civilians.
I will solve the problems with you. We will do it calmly. Don't listen to our enemies," the governor said in a post on Telegram.