What are the armed groups that 'penetrated Russia?'

STORY: Russia's military says it's routed an incursion by armed militants who penetrated a Russian border region with armored vehicles, sparking at least two days of battles and civilian evacuations in what appears to be one of the biggest incursions by pro-Ukraine fighters of the war.

It happened in the Belgorod area and this video released by the defense ministry is said to show the intensity: multiple explosions and what appear to be artillery or air strikes on their own soil.

Moscow says it killed over 70 militants they say are Ukrainian but the two groups claiming responsibility say they're actually Russian nationals against Putin's government, and their exact relationship to Kyiv is unclear.

So who are these groups and what is known about them?

The first group is called the Russian Volunteer Corps, or RVC, and was founded by a far-right Russian national last August. It's composed of Russians who have been fighting for Ukraine against their own country.

This video shows one of their fighters slapping a bumper sticker on an armored personnel carrier they say they captured inside Russia.

Ukraine's military intelligence agency says the RVC is an independent underground group inside Russia that also has a unit in the Ukrainian foreign legion, but the Foreign Legion says it has nothing to do with the RVC.

The second group is called the Freedom of Russia Legion, which says it was formed in spring last year and is also composed of Russians.

In this video a purported member is saying they want their children to grow up in a Russia free from corruption, censorship, restrictions on freedom and repression.

It says it operates under Ukrainian command, but Ukraine's military intelligence agency wouldn't confirm or deny that forces in Belgorod are a Ukrainian unit.

The regional governor says an elderly woman was killed during evacuations from the fighting and eight wounded.