Russia confirmed Friday it carried out an air strike on Kyiv during a visit by the UN chief, the first such attack on the Ukrainian capital in nearly two weeks, and in which a journalist also died.

Vera Gyrych, a producer for the US-funded Radio Free Europe/Radio Liberty, died when a Russian missile slammed into the building where she lived in Kyiv, the media group said.

Russia's defence ministry said it had deployed "high-precision, long-range air-based weapons" that it added "have destroyed the production buildings of the Artyom missile and space enterprise in Kyiv".

Ukraine's President Volodymyr Zelensky said the strikes, which immediately followed his talks with Guterres, were an attempt by Russia "to humiliate the UN and everything that the organisation represents".

Earlier that day, UN Secretary-General Antonio Guterres had toured Bucha and other suburbs of Kyiv where Moscow is alleged to have committed war crimes. Russia denies killing civilians.

Germany condemned the "inhumane" attack that showed Russian President Vladimir Putin has "no respect whatsoever for international law".

Kyiv mayor Vitali Klitschko said there had been "two hits in the Shevchenkovsky district", with one hitting "the lower floors of a residential building". 

The powerful blast had ripped out walls and doors, leaving piles of rubble on the ground. 

Mykhailo Vovchynskyi, who had just moved into the destroyed building, said that if the Russian deemed that to be a "high-precision attack, that is pretty cynical".

"It's inhuman behaviour," the 22-year-old told AFP.

"I think Russians aren't afraid of anything, not even the world's judgement," Anna Hromovych, deputy director of a heavily damaged clinic, told AFP as she and others were cleaning up the devastation on Friday.

More than 8,000 alleged war crimes 

"It is a war zone, but it is shocking that it happened close to us," said Saviano Abreu, spokesman for the UN's humanitarian office who was travelling with Guterres, adding that the delegation was safe.

Guterres, who was in Kyiv after talks in Moscow with Putin, had called war "evil" after visiting Bucha and demanded the Kremlin cooperate with an International Criminal Court investigation into the accusations.

Ukrainian prosecutors said they have pinpointed more than 8,000 alleged war crime cases and have opened investigations into 10 Russian soldiers for suspected atrocities in Bucha, where dozens of bodies in civilian clothes were found following Moscow's retreat.

Those cases involve "killing civilians, bombing of civilian infrastructure, torture" and "sexual crimes" reported during Russia's occupation of various parts of Ukraine, prosecutor general Iryna Venediktova told a German broadcaster. 

Britain will send a team of experts on war crimes in May to help Ukrainian investigators as they compile evidence and witness statements, said Foreign Secretary Liz Truss. 

"We're also using British intelligence to help show the links between what is happening on the front line and the Russian authorities because it's important that everybody in the chain of command is held to account," she added.

Three months into an invasion that failed in its short-term aim of capturing Kyiv, Russia is now intensifying operations in the breakaway eastern Donbas region and tightening its noose around the devastated strategic southern port city of Mariupol.

Ukrainian authorities said they planned to evacuate civilians Friday from the besieged Azovstal steel plant, the last holdout in Mariupol where hundreds of people are sheltering with Ukrainian troops.

Mariupol shelling 

In an early morning statement on Telegram, defenders of the factory said shelling had struck a field hospital inside the plant, causing it to collapse.

"Among the already wounded servicemen are dead, newly wounded and injured," the statement said without providing specific casualty numbers.

With the war claiming thousands of lives, Kyiv has admitted Russian forces have captured a string of villages in the Donbas region.

But Ukrainian forces, which have been armed by Western allies, also reported small victories elsewhere along the frontline. 

In the region of Kharkiv, Ukrainian forces said they recaptured a key village, Ruska Lozova, from the Russians.

"This is a strategically important settlement on the Kharkiv-Belgorod motorway. It is the settlement from which the enemy carried out aimed fire on civilian infrastructure and residential districts of Kharkiv during siege," Ukraine's army command said.

More Western armaments are due to arrive in Ukraine, with US President Joe Biden on Thursday seeking a $33 billion aid package for the country. 

The bulk -- $20 billion -- would be weapons and other security assistance, while $8.5 billion will be economic aid.

"The cost of this fight is not cheap. But caving to aggression is going to be more costly if we allow it to happen," said Biden, whose announcement was hailed by Zelensky as an "important step"

A senior US official, speaking on condition of anonymity, said the spending package would keep Ukraine's government and military going through to the start of October.

While Biden said the United States was sending 10 anti-tank weapons for every Russian tank, Ukraine's air force commander said his country's anti-aircraft systems were unable to strike higher altitude bombers.

British exercises 

"We need medium and long-range anti-aircraft systems" and "modern fighters", said Mykola Olechchuk.

Britain meanwhile said it was deploying about 8,000 troops for exercises across eastern Europe in a show of Western allies' resolve against Russian aggression.

The cost of the war has reverberated across Europe, with Brussels publishing data showing that output growth for the eurozone has slowed to 0.2 percent, while consumer prices have leapt by a record 7.4 percent in April.

But that pales in comparison to the plight of Ukrainians, more than 5.4 million who have fled their country since the invasion, according to UN estimates.

Another 7.7 million others are displaced internally, the IOM said, appealing for $514 million to help.

"We're left with only one hope: to return home," said pensioner Galina Bodnya in the southern city of Zaporizhzhia.