Kyiv: An explosion has "seriously damaged" Russia's Black Sea flagship, which is leading the naval assault on Ukraine, state media claimed on Thursday, as Moscow vowed to target Kyiv's command centres.

As the conflict enters its seventh week, US Vice President Joe Biden unveiled an $800 million military aid package for Ukraine, which includes helicopters and armoured personnel carriers.

International prosecutors have suggested that the fighting has turned Ukraine into a "crime scene," implying that those responsible may face charges in the future.

The Moskva missile cruiser was damaged by ordnance that detonated "as a result of a fire," according to the Russian defence ministry, which added that the cause of the fire was being probed.

Early in the conflict, the Moskva acquired renown when it demanded capitulation from Ukrainian border forces defending the vital Snake Island, only to be vehemently rebuffed.

It was originally stationed in Syria, where it provided naval support to Russian forces at the Hmeimim airfield.

The crew had been evacuated, but "the ship was substantially damaged," according to Russian state media.

Russia has met tremendous resistance and now even reprisals in its territory, prompting Moscow to threaten to target command centres in Kyiv if Ukraine continues to launch strikes on Russian soil.

The threat sent shockwaves across Kyiv, which had been enjoying some reprieve after Russian forces retreated from the region after failing to secure the city.

Moscow was thought to be redirecting its military efforts in Ukraine to the south and east, with Ukrainian authorities warning of brutal new fighting in the eastern Donbas region.

The US aid package, which was presented on Wednesday, includes armoured personnel carriers and helicopters, as well as other equipment that Washington had previously refused to deliver to Ukraine for fear of worsening the confrontation with nuclear-armed Russia.

As Ukraine prepared for an escalation of bloodshed, the Pentagon said it was trying to arm the country with weaponry that would "give them a little more range and distance."