KYIV, Ukraine (NewsNation/ AP) — Talks to stop the fighting in Ukraine resumed Friday, as another desperate attempt to rescue civilians from the shattered and encircled city of Mariupol failed and Russia accused the Ukrainians of a cross-border helicopter attack on a fuel depot.

The governor of Russia’s Belgorod region, Vyacheslav Gladkov, said a fiery raid on Russian soil by two helicopter gunships left two people wounded, though state oil company Rosneft denied anyone was hurt.

“Certainly, this is not something that can be perceived as creating comfortable conditions for the continuation of the talks,” Kremlin spokesman Dmitry Peskov said, five weeks after Moscow began sending upwards of 150,000 of its own troops across Ukraine’s border.

The Russian claim could not immediately be verified. Ukrainian Foreign Minister Dmytro Kuleba said he could “neither confirm nor reject the claim that Ukraine was involved in this, simply because I do not possess all the military information.”

Ukrainian President Volodymyr Zelenskyy warned his people that retreating Russian forces were creating “a complete disaster” outside the capital as they leave mines across “the whole territory,” even around homes and corpses.

Ukraine denied responsibility for the fiery blast, but if Moscow’s claim is confirmed, it would be the war’s first known attack in which Ukrainian aircraft penetrated Russian airspace.

Also on Friday, the U.S. Defense Department announced it is providing an additional $300 million in military equipment to Ukrainian forces amid Russia’s invasion.

Pentagon press secretary John Kirby said in a statement that the gear in the new package would include laser-guided rocket systems, armored vehicles, and night vision devices.

This brings the total to $2.3 billion that the U.S. administration has provided Ukraine.

Meanwhile, Russian troops continued withdrawing from areas around Kyiv, three days after Moscow said it would reduce military activity near the Ukrainian capital and the northern city of Chernihiv to promote trust between the two sides. And Ukrainian forces exploited the pullback by mounting counterattacks and retaking towns and villages.

But Ukraine and its allies warned that the Kremlin is not de-escalating but resupplying its troops and redeploying them to the country’s east for an intensified assault on the predominantly Russian-speaking Donbas region, which includes Mariupol.

The latest negotiations, taking place by video, follow a meeting Tuesday in Turkey, where Ukraine reiterated its willingness to abandon a bid to join NATO and declare itself neutral — Moscow’s chief demand. In return, Ukraine proposed that its security be guaranteed by several other countries.

The head of the Russian delegation, Vladimir Medinsky, wrote on social media that Moscow’s positions on retaining control of the Crimean Peninsula — seized from Ukraine in 2014 — and expanding the territory in eastern Ukraine held by Russia-backed separatists “are unchanged.”

The invasion that has left thousands dead and driven more than 4 million refugees from Ukraine.

On the outskirts of Kyiv, where Russian troops have withdrawn, damaged cars lined the streets of Irpin, a suburban area popular with young families, now in ruins. Emergency workers carried elderly people on stretchers over a wrecked bridge to safety.

Three wooden crosses next to a residential building that was damaged in a shelling marked the graves of a mother and son and an unknown man. A resident who gave her name only as Lila said she helped hurriedly bury them on March 5, just before Russian troops moved in.

“They were hit with artillery and they were burned alive,” she said.

An Irpin resident who gave his name only as Andriy said the Russians packed up their equipment and left on Tuesday. The next day, they shelled the town for close to an hour before Ukrainian soldiers retook it.

“I don’t think this is over,” Andriy said. “They will be back.”

To the south, the International Committee for the Red Cross said it was unable to carry out an operation to bring civilians out of Mariupol by bus. It said a team had been on its way but had to turn back.

City authorities said the Russians were blocking access to Mariupol.

“We do not see a real desire on the part of the Russians and their satellites to provide an opportunity for Mariupol residents to evacuate to territory controlled by Ukraine,” Petro Andryushchenko, an adviser to the mayor of Mariupol, wrote on the Telegram messaging app.

He said Russian forces “are categorically not allowing any humanitarian cargo, even in small amounts, into the city.”

The strategic port city on the Sea of Azov has seen some of the worst suffering of the war, with weeks of heavy fighting and shortages of water, food, fuel and medicine. Around 100,000 people are believed left in the city, down from a prewar 430,000.

“We are running out of adjectives to describe the horrors that residents in Mariupol have suffered,” Red Cross spokesperson Ewan Watson said.

On Thursday, Russian forces blocked a 45-bus convoy attempting to evacuate people from Mariupol, and only around 600 people were able to leave in private cars, the Ukrainian government said. Russian forces also seized 14 tons of food and medical supplies bound for Mariupol, Deputy Prime Minister Iryna Vereshchuk said.

In the past few days, the Kremlin, in a seeming shift in its war aims, said its “main goal” is gaining complete control of the Donbas. Mariupol’s capture would be a major prize for the Russians, giving them an unbroken land bridge to Crimea.

The Donbas is the industrial region of eastern Ukraine where Moscow-backed separatists have been battling Ukrainian forces since 2014. The separatists have declared two areas independent republics.

Despite its pledge to scale back, Russian forces have continued to bombard both the Chernihiv area and cities on the outskirts of Kyiv. But Ukraine’s military said it had retaken 29 settlements in the two regions amid a Russian withdrawal of some of its troops.

Russian forces in the northeast also continued to shell Kharkiv, and in the southeast sought to seize the cities of Popasna and Rubizhne as well as Mariupol, the Ukrainian military said.

Russian President Vladimir Putin’s forces also withdrew from the heavily contaminated Chernobyl site in northern Ukraine early Friday.

Ukraine’s state power company, Energoatom, said Russian soldiers had received “significant doses” of radiation from digging trenches in the exclusion zone around the closed nuclear power plant. But the International Atomic Energy Agency said it could not independently confirm that, and there was no immediate comment from the Kremlin.

Energoatom gave no details on the condition of the soldiers and did not say how many were affected.