Fighting in Russia's western Belgorod region entered a second day on Tuesday following a military incursion from Ukraine. Russia has blamed Ukrainian armed groups and launched a terrorism investigation.
Kyiv has denied any role and said the attackers are Russian citizens. Two groups - the Russian Volunteer Corps (RVC) and Freedom of Russia Legion - have claimed responsibility. Here is what we know about them.
RUSSIAN VOLUNTEER CORPS
The RVC was founded by a far-right Russian national last August and comprises Russians who have been fighting in and for Ukraine against their own country.
The group has also been active over the border in Russian territory, and claimed responsibility for a raid there in March as well as the incursion into Belgorod.
The Ukrainian military intelligence agency says the RVC is an independent underground group inside Russia that also has a unit in the Ukrainian Foreign Legion. The Foreign Legion says it has nothing to do with the RVC.
A video posted by the RVC on Monday showed two men claiming to have captured a Russian armoured personnel carrier. Reuters was able to identify one of the men as Ilya Bogdanov, a Russian national who received Ukrainian citizenship in 2015 after fighting for Kyiv against Russian-backed forces in Ukraine's east.
FREEDOM OF RUSSIA LEGION
The Freedom of Russia Legion says it was formed in spring 2022 "out of the wish of Russians to fight in the ranks of the Armed Forces of Ukraine against Putin's armed gang".
It says it cooperates with the Ukrainian armed forces and operates under Ukrainian command. It has claimed responsibility for the attack in Belgorod and says it has been fighting in eastern Ukraine.
The Ukrainian military intelligence agency's spokesperson said on Monday that the attacks in Belgorod only involved Russian citizens and that they were creating a "security zone" to protect Ukrainian civilians. He did not confirm or deny that the forces operating there are a Ukrainian unit. The agency did not immediately respond to a request for clarification.
