Ukraine says civilians killed in fresh Russian shelling

Deadly Russian air strikes hit a residential block in Ukraine's second city of Kharkiv and the main TV tower in the nation's capital, Kyiv said Tuesday, with Ukraine's president accusing the Kremlin of a "war crime" as the civilian toll of the invasion mounted.

Despite sanctions and warnings of a humanitarian crisis, the fresh assaults on day six of Russia's invasion came as a massive military convoy was closing on the capital, and Moscow warned terrified residents living near security infrastructure to leave their homes.

"This is state terrorism on the part of Russia," charged Ukrainian President Volodymyr Zelensky, accusing Moscow of committing a "war crime" in Kharkiv.

After a call with US President Joe Biden -- who was later to deliver a State of the Union address overshadowed by the spiralling Ukraine conflict -- Zelensky tweeted: "We must stop the aggressor as soon as possible." 

Although Russia has denied targeting civilian infrastructure, British Prime Minister Boris Johnson on Tuesday called the bombardment of Kharkiv "absolutely sickening" and reminiscent of massacres of civilians in Sarajevo in the 1990s.

Eight people were reported killed in the strike on a residential building in the city, Ukraine's second largest, and officials said 10 people had been killed by Russian shelling on a local government complex.

The Kyiv TV tower strike killed five people and knocked out some state broadcasting, Ukrainian officials said, but left the structure intact.

The International Criminal Court has already opened a war crimes investigation against Russia. Ukraine says more than 350 civilians, including 14 children, have been killed in the conflict.

In southern Ukraine, the city of Mariupol on the Azov Sea was left without electricity after bombardment, while Kherson on the Black Sea reported Russian checkpoints encircling the city.

In a key victory for Moscow, Russia's defence ministry said its troops had linked up with pro-Moscow rebel forces from eastern Ukraine along the Azov Sea coast.

But Ukrainian forces say despite incursions by "sabotage groups," Russian forces have yet to capture a major city.