Volodymyr Zelensky rewards a member of the National Guard in Kyiv. Reuters

President Volodymyr Zelensky urged the West to give Ukraine tanks, planes and missiles to help fend off the Russian forces, which the Kyiv government said were increasingly targeting fuel and food depots.

A child holds a sign during a rally in support of Ukraine in New York City on Saturday. AFP

Meanwhile, US officials continued efforts to soften comments on Saturday from US President Joe Biden, who said in a fiery speech in Poland that Russian leader Vladimir Putin "cannot remain in power."

US Secretary of State Antony Blinken said Washington had no strategy of regime change in Moscow, telling reporters in Jerusalem that Biden had simply meant Putin could not be "empowered to wage war" against Ukraine or anyone else.

After more than four weeks of conflict, Russia has failed to seize any major Ukrainian city and Moscow signalled on Friday it was scaling back its ambitions to focus on securing the Donbass region of eastern Ukraine, where Russian-backed separatists have been fighting the Ukrainian army for the past eight years.

A local leader in the self-proclaimed Luhansk People's Republic said on Sunday the region could soon hold a referendum on joining Russia, just as happened in Crimea after Russia seized the Ukrainian peninsula in 2014.

Crimeans voted overwhelmingly to break with Ukraine and join Russia — a vote that much of the world refused to recognise.

"In fact, it is an attempt to create North and South Korea in Ukraine," Kyrylo Budanov, the head of Ukrainian military intelligence, said in a statement, referring to the division of Korea after World War Two. He predicted Ukraine's army would push back Russian forces.

"In addition, the season of a total Ukrainian guerrilla safari will soon begin. Then there will be one relevant scenario left for the Russians, how to survive," he said.

HEAVY ARMOUR

Moscow says the goals for what Putin calls a "special military operation" include demilitarising and "denazifying" its neighbour. Ukraine and its Western allies calls this a pretext for an unprovoked invasion. The invasion has devastated several Ukrainian cities, caused a major humanitarian crisis and displaced an estimated 10 million people, nearly a quarter of Ukraine's total population.

In a late-night television address on Saturday, Zelensky demanded that Western nations hand over military hardware that was "gathering dust" in stockpiles, saying his nation needed just 1% of Nato's aircraft and 1% of its tanks.

Western nations have so far given Ukraine anti-tank and anti-aircraft missiles as well as small arms and protective equipment, but have not offered any heavy armour or planes.

This photo shows a funeral procession for a Ukrainian serviceman in Yuzhne, Odessa region, Ukraine. AP

"We've already been waiting 31 days. Who is in charge of the Euro-Atlantic community? Is it really still Moscow, because of intimidation?" Zelensky said, suggesting Western leaders were holding back on supplies because they were frightened of Russia.

Ukrainian Interior Ministry adviser Vadym Denysenko said on Sunday that Russia had started destroying Ukrainian fuel and food storage centres, meaning the government would have to disperse stocks of both in the near future.

Appearing to confirm that, the Russian defence ministry said its missiles had wrecked a fuel deposit on Saturday as well as a military repair plant near the western city of Lviv, just 60km from the Polish border.

In its latest military assessment, the British Ministry of Defence said Russian forces appeared to be concentrating their efforts on encircling Ukrainian troops directly facing separatist regions in the east.

"The battlefield across northern Ukraine remains largely static with local Ukrainian counterattacks hampering Russian attempts to reorganise their forces," the ministry said.

HISTORIC STRUGGLE

Biden drew criticism for his improvised remarks during a speech in Warsaw that sought to frame the war as part of a historic struggle for democratic freedoms.

"For God's sake, this man cannot remain in power," Biden said of Putin. Earlier he called the Russian leader a "butcher."

Veteran US diplomat Richard Haass, president of American think-tank the Council on Foreign Relations, said on Twitter the comments made "a dangerous situation more dangerous."

US officials tried to walk back the president's words, with a White House official saying they were not a call for Putin's removal, but rather meant that he should not be allowed to exercise power over his neighbours or the region.

USSecretary of State Blinken echoed the sentiment. "As you know, and as you have heard us say repeatedly, we do not have a strategy of regime change in Russia — or anywhere else, for that matter," he said in occupied Jerusalem.

The United Nations has confirmed 1,104 civilian deaths and 1,754 injuries across Ukraine but says the real toll is likely to be higher. Ukraine said on Sunday 139 children had been killed and more than 205 wounded so far in the conflict.

Ukrainian Air Force spokesman Colonel Yuri Ignat told Reuters the country's pilots had trained for years and conducted joint exercises with US pilots precisely because "we understood that there could be such a scenario."

Ukraine now needs fighter jets such as American F-15s and F-16s to supplement Ukraine's ageing Soviet-era MiG-29s and Sukhoi planes, he said, in order to overcome Russia's numerical and technological superiority in the air.

"We are fighting with the equipment of the '70s and '80s, they are fighting with the equipment of 2010 and later," Ignat said.

"We would be grateful for the Soviet-made equipment offered to us by the countries of Central Europe which still have it. But it will not be enough," he said.

"We would also like to have Western planes, such as F15, F16. We don't ask for anything more, like the F35," Ignat added, referring to a more modern model of US combat aircraft.