A Russian strike on a school sheltering civilians claimed 60 lives, Ukraine said Sunday, as the G7 reaffirmed their unity with Kyiv on the eve of Moscow's plans for a flashy World War II victory commemoration.

As intense fighting continued, Ukrainian President Volodymyr Zelensky confirmed the death toll in Saturday's Russian air strike on a school in the eastern village of Bilogorivka. That would be one of the highest one-day tolls since Russia invaded on February 24.

Russian President Vladimir Putin leads commemorations Monday of the Soviet Union's defeat of Nazi Germany, but Ukraine, under unrelenting attack, is desperate to deny Moscow any sense of military invigoration.

Severodonetsk, in eastern Ukraine, was once a busy industrial city of 100,000, but is now all but abandoned as the last pocket defended by Kyiv's forces in the Lugansk region
Severodonetsk, in eastern Ukraine, was once a busy industrial city of 100,000, but is now all but abandoned as the last pocket defended by Kyiv's forces in the Lugansk region AFP / Yasuyoshi CHIBA

Putin is expected to flaunt Russia's military might during the symbolically important event. Huge intercontinental ballistic missiles will be towed for official review through Moscow's Red Square, and a planned flyover will feature fighter jets in a "Z" formation showing support for the war.

The Victory Day parade is a longtime tradition in Russia, but Monday's has taken on great prominence as Putin seeks to justify a war that has gone on far longer -- and at far higher cost -- than expected.

Putin has sought to legitimise the invasion by comparing it with the previous struggle against Nazism and the national pride it brought.

Russian forces have encountered tough resistance from Ukrainian defenders, but hope to snatch some symbolic wins ahead of Monday's Victory Day parade in Moscow
Russian forces have encountered tough resistance from Ukrainian defenders, but hope to snatch some symbolic wins ahead of Monday's Victory Day parade in Moscow AFP / Yasuyoshi CHIBA

"Today, our soldiers, as their ancestors, are fighting side by side to liberate their native land from the Nazi filth with the confidence that, as in 1945, victory will be ours," Putin said.

Zelensky also marked the end of the 1939-1945 war by comparing Ukraine's battle for national survival to the region's war of resistance against its former Nazi occupiers.

"Decades after World War II, darkness has returned to Ukraine, and it has become black and white again," he said, in a monochrome social media video shot before a bombed-out apartment block.

Zelensky said later in his nightly video address that the school attack showed "Russia has forgotten everything that was important to the victors of World War II."

Russian invasion
Russian invasion AFP / Simon MALFATTO

In the latest shows of Western support, US First Lady Jill Biden and Canadian Prime Minister Justin Trudeau made unannounced visits to Ukraine, and G7 leaders joined Zelensky on a video call before pledging new backing -- including a key vow to ban or phase out imports of Russian oil.

The Victory Day parade in Moscow on May 9 is an annual celebration of the Soviet Union's defeat of Nazi Germany in World War II, but this year Moscow will also associate it with its campaign in Ukraine
The Victory Day parade in Moscow on May 9 is an annual celebration of the Soviet Union's defeat of Nazi Germany in World War II, but this year Moscow will also associate it with its campaign in Ukraine AFP / Kirill KUDRYAVTSEV

Britain announced more sanctions against Russia -- import tariffs on precious metals and export bans.

After Zelensky's video conference with G7 leaders, the group -- comprising Britain, Canada, France, Germany, Italy, Japan and the United States -- said in a statement that Putin's "unprovoked war of aggression" had brought "shame on Russia and the historic sacrifices of its people".

The White House said the G7 was "committed to phasing out or banning the import of Russian oil".

But EU diplomats will meet again next week to hammer out details of their latest sanctions package, after a proposed embargo on Russian oil exposed rifts in the bloc.

Russian shelling has been  intense in the east
Russian shelling has been intense in the east AFP / Yasuyoshi CHIBA

Separately, the White House said the United States would slap sanctions on three major Russian television stations and deny all Russian companies access to US firms' consulting and accounting services.

First Lady Biden met her Ukrainian counterpart Olena Zelenska at a school sheltering civilians, including children displaced by the conflict, near Ukraine's border with Slovakia.

"I wanted to come on Mother's Day," Jill Biden told reporters, saying she sought to demonstrate US support for Ukraine.

Map and photos charting Russian siege of Mariupol since start of March
Map and photos charting Russian siege of Mariupol since start of March AFP / Sylvie HUSSON

Meanwhile, depleted Ukrainian forces are bracing to defend their final bastion in the devastated port city of Mariupol.

Civilians have now been evacuated from Mariupol's Azovstal steelworks, witnesses said.

An AFP reporter in the city of Zaporizhzhia said Sunday that eight buses carrying 174 civilians -- including 40 evacuated from Azovstal -- had arrived in that Ukrainian-controlled city.

"The latest information that I have from both Ukraine and Russia is that there are no more civilians there (Azovstal), but we are not in a position to verify. We weren't inside the plant," Osnat Lubrani, the UN's humanitarian coordinator in Ukraine, told AFP.

More than 600 civilians have now been safely evacuated from the steelworks and other areas of Mariupol, the UN said.

This leaves a small force of defenders holed up in Azovstal's sprawling network of tunnels and bunkers.

"We hoped everyday for an evacuation," said Vladymyr Babeush, 41, an Azovstal evacuee who worked at the plant and was among those who arrived in Zaporizhzhia. "And now we are done waiting. We're so thankful to everyone involved."

"I'm very tired. I was in the bus for about 17 hours. But I feel happy because there's fresh air and I'm in Ukraine," said 17-year-old Azovstal evacuee Dmytro, who was wearing one of the plant's workers uniforms.

The complex -- the final pocket of Ukrainian resistance in the city -- has taken on symbolic value.

Full control of Mariupol would allow Moscow to create a land bridge between the Crimean peninsula, which it annexed in 2014, and eastern regions run by pro-Russian separatists.

In one of those regions, Lugansk, Ukrainian forces are now mounting a last-ditch defence of Severodonetsk, formerly an industrial city of 100,000 people.

Lugansk region governor Sergiy Gaiday said rescuers in Bilogorivka were searching for survivors in the debris left by the Russian attack on the school there, though the outlook was bleak.

"Bombs fell on the school," he said on Telegram, "and unfortunately it was completely destroyed."

Civilians who escaped Mariupol describe passing through Russian "filtration" sites where several evacuees told AFP they were questioned, strip-searched, fingerprinted, and had their phones and documents checked.

"But how can I rebuild it? How can I return there if the city of Mariupol doesn't exist anymore?"