A US Air Force officer palletises ammunition, weapons and other equipment bound for Ukraine. File/AP

Worth $150 million, the latest security assistance would include artillery munitions and radars, Biden said, as the country braces for fresh bombardment by Moscow's forces ahead of May 9, the day Russia celebrates the Soviet victory over the Nazis in the Second World War.

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A senior US official said the aid included counter-artillery radars used for detecting the source of enemy fire and electronic jamming equipment.

Friday's new batch brings the total value of US weaponry sent to Ukraine since the Russian invasion began to $3.8 billion.

An officer inspects cargo netting on palletised ammunition, weapons bound for Ukraine. AP

The president urged Congress to further approve a huge $33 billion package, including $20 billion in military aid, "to strengthen Ukraine on the battlefield and at the negotiating table."

The Pentagon meanwhile denied reports it helped Ukrainian forces sink the Russian warship Moskva in the Black Sea last month.

Pentagon spokesman John Kirby said the US had "no prior knowledge" of the plan to strike the ship, which sank leaving a still-unclear number of Russian sailors dead or missing.

While providing Ukraine with military aid, the United States has sought to limit knowledge of the full extent of its assistance to avoid provoking Russia into a broader conflict beyond Ukraine.

Biden, other G7 leaders, and Ukraine's President Volodymyr Zelensky are to meet virtually on Sunday to discuss Western support for Kyiv.

Azovstal evacuation

On Friday Zelensky said "diplomatic options" were also under way to rescue Ukrainian soldiers from the Mariupol steelworks, as civilian evacuations continued.

The Russian defence ministry said 50 people were evacuated from the site, including 11 children.

Around 200 civilians are estimated to still be trapped in the Soviet-era tunnels and bunkers.

It added they were handed over to the UN and Red Cross, which are assisting in the operation, and that the "humanitarian operation" would continue on Saturday.

About 200 civilians, including children, are estimated to still be trapped in the Soviet-era tunnels and bunkers beneath the sprawling Azovstal factory, along with a group of Ukrainian soldiers making their last stand.

Russia announced a daytime ceasefire at the plant for three days starting Thursday but the Ukrainian army said Russian "assault operations" had continued by ground and by air.

Ukraine's Azov battalion, leading the defence at Azovstal, said one Ukrainian fighter had been killed and six wounded when Russian forces opened fire during an attempt to evacuate people by car.

Azov battalion leader Andriy Biletsky wrote on Telegram that the situation at the plant was critical.

"The shelling does not stop. Every minute of waiting is costing the lives of civilians, soldiers, and the wounded."

May 9 fears

Ten weeks into a war that has killed thousands, destroyed cities and uprooted more than 13 million people, defeating the resistance at Azovstal and taking full control of strategically located Mariupol would be a major win for Moscow.

It would also be a symbolic success ahead of May 9, when Russia marks the anniversary of its 1945 defeat of Nazi Germany.

Ukraine's President Volodymyr Zelensky speaks in Kyiv. File photo

Ukrainian officials believe Moscow is planning a May 9 military parade in Mariupol, though the Kremlin has denied any such plans.

Officials have also said they expect the anniversary will coincide with an escalation of the war throughout the country.

"In the coming days, there is a high probability of rocket fire in all regions of Ukraine," mayor of Kyiv Vitali Klitschko said in a statement on social media.

"Be careful and follow the rules of security in wartime."

The eastern city of Odessa will also impose a longer curfew on May 8-9, its mayor said, as will Poltava in the country's centre.

White House Press Secretary Jen Psaki noted that the G7 meeting will come a day before "Victory Day" and the leaders will demonstrate "unity in our collective response".

"While (Russian President Vladimir Putin) expected to be marching through the streets of Kyiv, that's obviously not what's going to happen," Psaki said.

- Russia to remain 'forever' -

Since failing to take Kyiv early on in the war, Russia has refocused its offensive on the south and east of Ukraine.

Taking full control of Mariupol would allow Moscow to create a land bridge between the Crimean peninsula, which it annexed in 2014, and separatist, pro-Russian regions in the east.

In those regions, separatists said they had removed Ukrainian and English language traffic signs for Mariupol and replaced them with Russian ones.

Locals want to see proof that "Russia has come back here forever," said Denis Pushilin, head of the breakaway region of Donetsk.

In neighbouring Lugansk, Ukrainian officials said on Friday that Russian forces had almost encircled Severodonetsk — the easternmost city still held by Kyiv — and are trying to storm it.

Moscow is planning a May 9 military parade in Mariupol, though the Kremlin has denied any such plans.

Kherson in the south remains the only significant city Russia has managed to capture since the war began.

A senior official from the Russian parliament visiting the city on Friday also emphasised that Russia would remain in southern Ukraine "forever."

"There should be no doubt about this. There will be no return to the past," Andrey Turchak said.

'Peaceful solution'

On Friday, the UN Security Council unanimously adopted its first declaration on Ukraine since Russia invaded on February 24.

It backed Secretary General Antonio Guterres's efforts to find a "peaceful solution" to the war but stopped short of supporting a mediation effort led by him.

Russia then vetoed a resolution condemning the invasion and asking Moscow to move its army back to Russian soil.

UN Secretary General Antonio Guterres speaks during an event. File photo

Ukraine's Western allies have supported Kyiv with financial and military assistance, and have slapped unprecedented sanctions on Russia.

As European countries have sought to clamp down on Russian assets overseas, Italian authorities impounded a mega yacht as speculation swirled it might even belong to the Russian president.

"Scheherazade", worth an estimated $700 million, has been the subject of a probe into its ownership by Italy's financial police, which has helped "establish significant economic and business links" between the ship's owner and "eminent people in the Russian government".

Researchers at the anti-corruption foundation of Russian dissident Alexei Navalny have linked the yacht to Putin.

But the European Commission's proposal that all 27 EU members gradually ban Russian oil imports — a move that would have been its toughest yet — was dealt a blow on Friday when Hungary said it crossed a red line and should be sent back.

Agence France-Presse