Ukraine says it is investigating more than 21,000 war crimes and crimes of aggression allegedly committed by Russia since the start of its occupation.

Prosecutor General Iryna Venediktova told the BBC that she was receiving reports of 200 to 300 war crimes per day, Telegraph reports.

She admitted that many processes would be held in absentia, but emphasized that it was a "matter of justice" to continue with criminal prosecutions.

Russia invaded Ukraine on February 24.

The country denies all accusations of war crimes.

Speaking to the BBC's World Service programme, Venediktova warned that Russian soldiers who killed, tortured or raped civilians "must understand that it is only a matter of time before they will all be in court".

She said that although her team was working in regions across Ukraine, it was unable to investigate all cases "properly and effectively" due to a lack of access to some people and areas.

This was an obvious reference to the Ukrainian territories occupied by Russian troops.

In May, Venediktova said that around 600 suspects had already been identified and 80 criminal prosecutions had begun.

The first Russian soldier to stand trial in Ukraine, Sgt Vadim Shishimarin, was sentenced to life in prison for killing a civilian in May.

Ukraine says it has discovered multiple mass graves in Bucha, Borodyanka and other towns near the capital Kiev, which were briefly captured by Russian troops.