The Siberian Battalion, a pro-Ukraine militia group of Russian fighters, has shown its training to media outlets including NHK. The session was held at a training site in the Kyiv region on Wednesday.
The group says its members include male Russian nationals in their 20s to 60s who volunteered to fight against the Russian military.
About 30 of them, wearing bulletproof vests and helmets, underwent training in handling weapons and other military skills on the day.
The Siberian Battalion says it carried out a cross-border attack in the western Russian region of Belgorod last month, coinciding with Russia's presidential election. It claims the fighters temporarily took control of a municipal building.
A fighter in his 30s who says he joined the operation said its goal was to attack a place Russian forces had not expected would be targeted, obliging the enemy to pull troops from battlefronts in eastern and southern Ukraine. He said the battalion's goal is to end the regime of Russian President Vladimir Putin.
He said the battalion will fight against Russian forces whenever necessary, in Ukrainian or Russian territory.
Meanwhile, the governor of the Kharkiv region of eastern Ukraine said on social media on Wednesday that areas near the border suffered Russian shelling that killed three people, including a 14-year-old girl, and wounded two others.