The US Defense Department announced Friday it is allotting $300 million in "security assistance" for Ukraine to bolster the country's defense capabilities, adding to the $1.6 billion Washington has committed since Russia invaded in late February.

The package includes laser-guided rocket systems, drones, ammunition, night-vision devices, tactical secure communications systems, medical supplies and armored vehicles.

"This decision underscores the United States' unwavering commitment to Ukraine's sovereignty and territorial integrity in support of its heroic efforts to repel Russia's war of choice," Pentagon spokesman John Kirby said in a statement.

On Wednesday, US President Joe Biden and Ukrainian President Volodymyr Zelensky discussed "additional capabilities" to help the Ukrainian military, the White House said in a statement after the call.

In mid-March, Congress passed a funding bill that included $13.6 billion for humanitarian and military aid to Ukraine and NATO allies in eastern Europe.

Shortly after, Biden announced $1 billion in new security assistance to Ukraine.

A large portion of the military equipment the US has given to Ukraine has come from its own stockpile, through a process known as a "presidential drawdown."

Unlike that process, the $300 million announced Friday will go towards new contracts for military equipment from the Pentagon's defense industry partners.

One of the technologies included in the announcement is more Switchblade tactical drones.

Dubbed "kamikaze drones," Switchblades can be directed by an operator to find and, when ready, plunge onto a target, exploding on contact.

Kirby added that the US "also continues to work with its allies and partners to identify and provide to the Ukrainians additional capabilities."

Later Friday evening, the New York Times reported that following a request by Zelensky, the US had decided to facilitate the transfer of Soviet-made tanks from allies to Ukraine.

The decision would mark the first time the US has helped transfer tanks, though details about which countries would participate and how many tanks were being moved were not provided. 

Citing a US official, the report noted that the tanks will allow Ukraine to fire long-range artillery strikes against Russian targets in the eastern Donbas region.

Following weeks of fighting, Moscow said last week it will be focusing on the "liberation" of Donbas, where pro-Russian separatists have declared two independent republics.

Russia recognized the independence of the self-declared Donetsk and Lugansk People's Republics shortly before sending troops into Ukraine on February 24.

Kyiv silent on airstrike in Russia

Ukraine's president refused Friday to say whether he had ordered an airstrike on Russian soil, as a bus convoy navigated a tortuous evacuation to help thousands flee the besieged city of Mariupol.

Peace talks between Ukrainian and Russian officials resumed via video, but the Kremlin warned the helicopter attack on a fuel depot in the town of Belgorod would hamper negotiations.

Kyiv would not be drawn on whether it was behind the attack, with President Volodymyr Zelensky telling US network Fox News: "I'm sorry, I do not discuss any of my orders as commander in chief."

With the prospect of war expanding across Ukraine's borders, progress appeared stalled in one of the country's most pressing humanitarian disasters, in the shattered southern city of Mariupol.

But late Friday people who managed to flee Mariupol to Russian-occupied Berdiansk were from there carried on dozens of buses to Zaporizhzhia, some 200 kilometers (120 miles) to the northwest, according to an AFP reporter on the scene.

"I am just crying. I just saw my granddaughter," said Olga, who was waiting for relatives at a centre for displaced people in Zaporizhzhia.

"Her mother's family are still in Mariupol and we don't know if they are alive."

The evacuation of 3,071 people, according to figures announced by Zelensky, escaping the ferocious Russian shelling of Mariupol, was a rare success in a city that has faced weeks of bombardment.

At least 5,000 residents have been killed, according to local authorities, and the estimated 160,000 who remain face shortages of food, water and electricity.

The international Red Cross said a team heading to the city to conduct a separate evacuation effort was forced to turn back Friday after "arrangements and conditions made it impossible to proceed".

The Red Cross said its team will try again Saturday.

- Russia regrouping? -
After five weeks of a military campaign that has reduced parts of Ukraine to rubble, Moscow said this week it would scale back attacks on the capital Kyiv and the city of Chernigiv.

But Zelensky said Russia was consolidating and preparing "powerful strikes" in the east and south, joining a chorus of Western assessments that Moscow troops were regrouping, not withdrawing.

On Friday he played host to European Parliament President Roberta Metsola in Kyiv, hailing her "heroism" for visiting the war zone.

"We are glad that you are on the side of the light and the good," Zelensky told Metsola.

"Courage, strength, resolve," Metsola said on Twitter, posting a photograph of her and Zelensky shaking hands.

The airstrike in Russia hit energy giant Rosneft's fuel storage facility in the western town of Belgorod, around 40 kilometres (25 miles) from the border with Ukraine.

Oleksiy Arestovych, an aide to Ukraine's president, said in a Twitter video that "for what's happening on Russia's territory, the responsibility lies with Russia, and it's up to them to deal with." 

But the consequence on peace negotiations was swiftly made clear by Moscow.

"This is not something that can be perceived as creating comfortable conditions for the continuation of negotiations," Kremlin spokesman Dmitry Peskov told reporters.

Russia launched its invasion on February 24, expecting to quickly take Kyiv and topple Zelensky's government. 

A ferocious Ukrainian fightback and Russia's logistics and tactical problems scuppered such plans, with Russia also battling unprecedented Western sanctions that have led multinationals to quit the country en masse.

US officials Friday gave a grim assessment of Russia's economy, warning it will tumble into a "deep" recession and shrink by 10 percent. 

On the ground, Ukraine's troops were beginning to reassert control including around capital Kyiv and in the southern region of Kherson -- the only significant city that Russia had managed to occupy.

Kyiv has grown impatient over the West's reluctance to step up and provide greater military support to Ukraine, with Washington and other capitals concerned about an escalating conflict with nuclear-armed Russia.

"Just give us missiles. Give us airplanes," Zelensky pleaded on Fox. "You cannot give us F-18 or F-19 or whatever you have? Give us the old Soviet planes. That's all... Give me something to defend my country with."

- 'Common grave' -
Ukraine's defence ministry meanwhile said Russian troops were continuing their "partial retreat" from the north of Kyiv towards the Belarusian border. 

Civilians have trickled out of devastated areas as Ukrainian forces liberated areas around Kyiv and Chernigiv.

Three-year-old Karolina Tkachenko and her family had walked an hour through a field strewn with burnt-out Russian armoured vehicles to flee their village outside Kyiv.

"The shops are closed, there's no delivery of supplies. The bridge is also blown up, we can't go for groceries through there," said Karolina's mother Karina Tkachenko. 

"I hope all this will end soon, and I will go back to my work," she told AFP.

In Mariupol, Viktoria Dubovytskaya, who had sheltered in the theatre where 300 people are feared to have been killed in Russian bombardments, said she only grasped the extent of the destruction as she fled.

Bodies lay in the rubble, and small wooden crosses were planted in the ground, she told AFP.

"When people find their loved ones, they just bury them wherever they can. Sometimes where roses used to bloom," she said. "The city is now a common grave."

- Radiation risks -
The UN's cultural agency said Friday it has confirmed at least 53 Ukrainian historical sites, religious buildings and museums have sustained damage during the invasion.

Ukraine also warned that Russian forces who left Chernobyl nuclear plant -- site of the world's worst nuclear accident, in 1986 -- after weeks of occupation may have been exposed to radiation.

"Russia behaved irresponsibly in Chernobyl" by digging trenches in contaminated areas and keeping plant personnel from performing their duties, said Foreign Minister Dmytro Kuleba. 

Latest developments

Here are the latest developments in the war in Ukraine:

- Mariupol evacuation postponed -
The Red Cross says it is "impossible to proceed" with the planned evacuation of civilians from the besieged Ukrainian city of Mariupol on Friday.

An ICRC team of three vehicles and nine personnel sent to facilitate the evacuation of thousands of civilians has been forced to turn around and "will try again on Saturday", it says.

- Peace talks resume -
Peace talks between Ukrainian and Russian officials resume via video, but Moscow warns that the helicopter attack will hamper negotiations.

Moscow's chief negotiator Vladimir Medinsky says on Telegram: "Our positions on Crimea and Donbass have not changed."

- 'Russia preparing powerful strikes' -
Ukraine's President Volodymyr Zelensky says Russia is preparing "powerful strikes" in the country's east and south, including Mariupol.

Moscow said in peace talks earlier this week it would scale back attacks on the capital Kyiv and the northern city of Chernigiv.

- Ukrainian troops regaining control - 
Ukraine's troops begin to regain control including around the capital Kyiv and in the southern region of Kherson -- the only significant city that Russia had managed to occupy.

Russian troops "are continuing their partial retreat" from the north of Kyiv towards the Belarusian border, Ukraine's defence ministry says.

- New gas war front -
Russian President Vladimir Putin says "unfriendly" countries, including all EU members, must set up ruble accounts to pay for gas deliveries from April, or "existing contracts would be stopped". 

- 30 countries tap oil reserves -
The 31-country International Energy Agency (IEA) agrees to tap national emergency oil reserves again in a bid to calm crude prices that have soared following Russia's invasion of Ukraine.

On Thursday US President Joe Biden announced a record release of US oil onto the market.

- China warned -
The EU's top officials have warned China's leaders at a summit not to help Russia wage war on Ukraine or sidestep Western sanctions, European Commission head Ursula von der Leyen says. 

"It would lead to a major reputational damage for China here in Europe," Von der Leyen says after video talks with Chinese President Xi Jinping.

- Chernobyl radiation -
Russian soldiers were likely exposed to radiation while they were occupying the area around the Chernobyl nuclear power station over the past four weeks, Ukraine's nuclear agency Energoatom says.

The power station, the site of the world's worst nuclear disaster in 1986, was taken back under the control of Ukrainian forces on Thursday.

- Lavrov lauds India -
Russia's foreign minister Sergei Lavrov praises India's refusal to condemn the Ukraine invasion, stressing their "friendship" and saying Moscow and New Delhi will find ways to circumvent "illegal" Western sanctions and continue to trade.

- Landmarks damaged -
The UN's cultural agency UNESCO says it has confirmed that at least 53 Ukrainian historical sites, religious buildings and museums have sustained damage during Russia's invasion of the country.

- 4.1 million refugees -
The number of Ukrainian refugees fleeing Russia's war in their country has crossed 4.1 million, the United Nations says.