Ukraine urges halt to Russia's assault as Biden heads to Poland

President Volodymyr Zelenskiy said on Friday that Ukrainians "need to achieve peace" and halt Russian bombardment that has forced millions to flee to countries like Poland, where US President Joe Biden is due to visit and witness the crisis first hand.

On the heels of leaders' summits in Brussels that aimed to show a united Western front against Russia's month-long invasion of its neighbour, Biden goes to Poland on Friday to meet with experts involved in the refugee response.

After announcing new military and humanitarian aid on Thursday in Brussels, Western leaders denounced Moscow's invasion as barbaric while the United States and Britain expanded sanctions on Russia to new targets.

The Russian invasion, which President Vladimir Putin calls a "special operation", has killed thousands of people, sent 3.6 million abroad and driven more than half of Ukraine's children from their homes, according to the United Nations.

Appearing exhausted in a brief video address early on Friday, Zelenskiy said he had made appeals to Western leaders "all for one reason - so that Russia understands that we need to achieve peace. Russia also needs to achieve peace".

Zelenskiy also said: "Every day we defend, we get closer to the peace we need so much ... and you can't stop for a minute. Because every minute is about our destiny, it is about our future. About whether we live."

The new Western aid stopped short of Zelenskiy's pleas for a full boycott of Russian energy and a no-fly zone over Ukraine where Moscow's bombs have blasted some residential areas into wastelands.

But Russia has so far failed to capture any major Ukrainian city in an assault it says is not designed to occupy territory but to destroy Ukraine's military capabilities.

Russia's shelling has been relentless but its armoured columns have barely moved in weeks, stalled near the capital Kyiv. In the east, however, Russian forces have laid siege to cities.

Russian forces have taken heavy casualties and are low on supplies, and US officials told Reuters that Russia is suffering failure rates as high as 60 per cent for some of its precision-guided missiles. 

The United States accused Russia of committing war crimes in Ukraine, allegations Russia denies. In video remarks released late on Thursday, Ukraine's Deputy Prime Minister Iryna Vereshchuk said Russian forces had tortured Ukrainian prisoners.

The allegations of torture could not be independently verified.

"We will find every Russian soldier who commits war crimes, along with their accomplices ... do not think that your surnames are unknown to us. No one will be able to escape punishment," Vereshchuk said.

CITIES UNDER SIEGE

Russia says its aims in Ukraine include capturing what it regards as dangerous nationalists. It also says that the NATO military alliance's eastern expansion threatens Russia's security.

Weeks of on-and-off peace talks between Russian and Ukrainian officials have failed to reach a breakthrough. Meanwhile, civilians have come under heavy Russian aerial assaults and artillery strikes.

In the besieged southern port of Mariupol, which lies between Russian-annexed Crimea and eastern areas held by Russian-backed separatists, thousands are in basements with scant water, food, medicine or power.

One woman waiting in line to receive food supplies in the city told Reuters her diabetic husband had slipped into a coma and died before the aid arrived. He was buried in a flowerbed. 

"We are planning on leaving but it's very difficult at the moment," the woman, who gave her name as Alexandra, said. "I can't leave my husband in a flowerbed ... And then we have nowhere to go."

Ukraine's armed forces chief of staff said on Thursday Russia was trying to resume offensives to capture Mariupol as well as Kyiv, Chernihiv, Sumy and Kharkiv, where hundreds have hunkered down inside metro stations to avoid Russian strikes. 

Still, Ukraine says it is shifting to the offensive and has pushed back Russian forces in some places. On Thursday, it said its forces had destroyed the Russian landing ship the "Orsk" at the Russian-occupied port of Berdyansk.

Russian officials did not immediately respond to requests for comment on the ship. Video footage showed smoke rising from a blaze at a dock and the flash of an explosion.

Civilians have managed to flee the fighting through humanitarian corridors negotiated by Ukrainian and Russian officials. Over 3,300 fled on Thursday, officials said.

Poland, home to the biggest Ukrainian refugee population in the region even before the war, has taken in more than 2.1 million people. Some plan to head elsewhere, but the influx has left public services struggling to cope. 

During his visit to the country, Biden will meet with President Andrzej Duda "to thank him for everything the people of Poland are doing and to discuss our coordinated humanitarian response to support the many Ukrainians who have been impacted by Putin's war," White House spokesperson Karine Jean-Pierre told reporters.