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.

"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?" Zelensky said in a video address late on Friday.

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 west beyond current lines, past the major Ukrainian coastal cities of Mykolaiv and Odesa.

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.

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

Moscow, it said, 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."

Russia says it is conducting a "special military operation" to demilitarise Ukraine and liberate its population from dangerous nationalists. Ukraine and its Western allies call Russia's Feb. 24 invasion an unjustified war of aggression.

Moldova's foreign ministry said it had summoned Moscow's ambassador on Friday to express "deep concern" about the general's comments. Moldova was neutral, it said. Moldova last month applied to join the European Union, charting a pro-Western course hastened by Russia's invasion.

U.S. State Department spokesperson Jalina Porter said Washington firmly supported Moldova's sovereignty.

Kremlin spokesman Dmitry Peskov declined to comment when asked if Russia had expanded the goals of its operation and how Moscow saw the political future of southern Ukraine.

As U.S. 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 authorized 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.

"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.

Ukraine's military said Russian forces had increased attacks along the frontline in the east and were attempting an offensive in the Kharkiv region, north of their main target, the Donbas.

Ukrainian military commands in the south and east said they had repelled 11 Russian attacks, killing up to 130 soldiers while destroying 12 tanks and 27 other armoured vehicles, details Reuters could not independently confirm.

Russia's defence ministry said its forces had captured a large arms depot in the Kharkiv region. It also reported hitting dozens of targets in the Donetsk and Kharkiv regions on Friday.

Ramzan Kadyrov, the leader of Russia's Chechnya region who has often described himself as Putin's "foot soldier", wrote on his official Telegram account late on Friday that Chechnya was deploying hundreds of additional volunteers to fight for Russia in Ukraine.

In Geneva, the United Nations human rights office said there was growing evidence of Russian war crimes, including indiscriminate shelling and summary executions. It said Ukraine also appeared to have used weapons with indiscriminate effects.

Russia denies targeting civilians and says, without evidence, that signs of atrocities committed by its soldiers were faked. Ukraine has previously said it will punish any soldiers found to have committed war crimes.

Russia said it had "securely blockaded" thousands of Ukrainian troops holed up in a huge steel works in Mariupol, the main port of the Donbas, a day after President Vladimir Putin said the army would not bother rooting them out.

Putin declared victory in the city after a nearly two-month siege. In a Russian-held section of Mariupol, dazed-looking residents ventured out this week to a background of charred apartment blocks and wrecked cars.

Volunteers in white hazmat suits and masks roved the ruins, collecting bodies from apartments and loading them on to a truck marked with the letter "Z", symbol of Russia's invasion.

Ukraine estimates tens of thousands of civilians have died in Russia's siege of the city and says 100,000 civilians are still there and need full evacuation.

Deputy Prime Minister Iryna Vereshchuk on Friday said "there is a possibility" a humanitarian corridor out of Mariupol could be opened up on Saturday.

U.N. Secretary-General Antonio Guterres will visit Moscow on Tuesday to meet Putin and discuss urgently bringing peace to Ukraine, a spokesperson said, adding that Guterres will then head to Kyiv for talks with Zelensky.

The U.S. military expects more than 20 countries to attend Ukraine-focused defense talks it will host in Germany next week that will focus in part on Kyiv's long-term defense needs, the Pentagon said on Friday.