Service members of pro-Russian troops stand guard in Mariupol, Ukraine, on Friday. Reuters

Russia and Ukraine hurtled toward what could be an epic battle for control of the country’s industrial heartland as Ukrainian officials reported that Moscow had shifted a dozen crack military units from the shattered port of Mariupol to eastern Ukraine.

Ukrainian President Volodymyr Zelensky warned that Russia's invasion of his country was just the beginning and that Moscow has designs on capturing other countries, after a Russian general said it wants full control over southern Ukraine.

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"All the nations that, like us, believe in the victory of life over death must fight with us. They must help us, because we are the first in line. And who will come next?" Zelenskiy said in a video address late on Friday.

Meanwhile, Russia reported on Friday that one serviceman was killed and 27 others were left missing after the fire on board the warship Moskva, which sank a week ago following what the Ukrainians boasted was a missile attack. The Russian military previously reported everyone aboard had been rescued.

A view shows an armoured vehicle destroyed during the Ukraine-Russia conflict in Mariupol, Ukraine, on Friday. Reuters

Also on Friday, new satellite images showed a second possible mass grave site in a town near Mariupol, where Ukrainian defenders are holed up in a steel plant.

As US Secretary of State Antony Blinken met Ukrainian Prime Minister Denys Shmyhal in Washington, Zelensky said allies were finally delivering the weapons Kyiv had asked for.

President Joe Biden said on Thursday he had authorised a further $800 million in military aid for Ukraine, including heavy artillery, ammunition and drones. Canada said on Friday it had provided more heavy artillery to Ukraine.

A senior EU official said the next couple of weeks would likely be decisive.

A man pushes his bicycle past a destroyed Russian armoured personnel carrier in Gostomel, Kyiv, Ukraine. AFP

"We are likely to see a very significant increase in the intensity of Russian military attacks in the east (and on) the coast," he told reporters.

The Russian Defence Ministry did not acknowledge an attack on the warship. It continued to say a fire broke out after ammunition detonated, without explaining how that happened. The loss of the guided missile cruiser – the flagship of Russia’s Black Sea fleet — was a humiliating setback for Moscow.

Rustam Minnekayev, deputy commander of Russia's central military district, was quoted by Russian state news agencies as saying full control over southern Ukraine would give it access to Transnistria, a breakaway Russian-occupied part of Moldova in the west.

That would cut off Ukraine's entire coastline and mean Russian forces pushing hundreds of miles further west, past the major Ukrainian coastal cities of Mykolaiv and Odesa.

Pedestrians walk past a damaged residential building in Gostomel, close to Kyiv, Ukraine, on Friday. AFP

The statement was one of the most detailed about Moscow's ambitions in Ukraine and suggests Russia does not plan to wind down its offensive there anytime soon.

In Mariupol, reduced largely to smoking rubble by weeks of bombardment, Russian state TV showed the flag of the pro-Moscow Donetsk separatists raised on what it said was the city's highest point, its TV tower. It also showed what it said was the main building at the city's besieged Azovstal steel plant in flames.

Ukraine's defence ministry said Minnekayev's comments showed Russia was no longer hiding its intentions.

Moscow, it said on Twitter, had now "acknowledged that the goal of the 'second phase' of the war is not victory over the mythical Nazis, but simply the occupation of eastern and southern Ukraine. Imperialism as it is."