Russia and Ukraine have conducted an exchange of prisoners, with 86 captives from each side returning home, Russian Human Rights Commissioner Tatyana Moskalkova said on Tuesday.

Moskalkova didn't go into details on the freed prisoners, but said Russia was now seeking the return of seamen and truckers from inside Ukraine.

Talks for an exchange involving four employees of Russia's State Atomic Energy Corporation, also known as Rosatom, failed at the last minute, according to Moskalkova. They remain in Ukraine.

"The four Rosatom employees that I asked the Ukrainian side about have been found. They are alive. Their whereabouts are unknown. They were on the exchange list, but at the last moment they were excluded," she said.

Ukrainian media outlet Ukrinform quoted Ukraine's Parliament Commissioner for Human Rights, Liudmyla Denisova, as saying that the female soldiers released from Russian captivity had been tortured and mistreated. Moscow hasn't yet responded to Kyiv's accusations.

The prisoner exchange happened as Ukrainian President Volodymyr Zelensky challenged the United Nations Security Council to "act immediately" or "dissolve yourself altogether" during a blistering address on Tuesday in which he showed harrowing footage of dead bodies. Zelensky called on the 15-member Security Council to expel Russia "so it cannot block decisions about its own aggression, its own war".

Dressed in his now trademark military green T-shirt, Zelensky, speaking via video from Kyiv, gave a chilling rendition of the "atrocities "he said were carried out by Russian troops against civilians in Bucha, a town outside the Ukrainian capital.

Claims rejected

Dmitry Medvedev, the former president and deputy chairman of the Russian Security Council, said the Bucha situation is another example of Ukraine's fake propaganda.

"Numerous PR agencies and 'troll factories' sponsored by Western governments and their tame nonprofits and NGOs get a lot of money for cooking it all up," Medvedev said.

Vasily Nebenzya, Russia's permanent representative to the United Nations, stressed Russia's forces have never targeted civilian facilities in the military operation.

Nebenzya told the UN council that Moscow places "on your conscience the ungrounded accusations against the Russian military, which are not confirmed by any eyewitnesses".

He also denied allegations made by Zelensky of mass deportations.

China's Ambassador to the UN Zhang Jun on Tuesday said the reports and images of civilian deaths in Bucha are deeply disturbing.

"The relevant circumstances and specific causes of the incident should be verified and established. Any accusations should be based on facts. Before the full picture is clear, all sides should exercise restraint and avoid unfounded accusations," he said.

A high-stakes meeting of NATO foreign ministers was taking place in Brussels on Wednesday, as US officials warned that Russia's actions in Ukraine could be entering a protracted new phase.

US Secretary of State Antony Blinken said it was "an important moment" to coordinate with allies and partners "on a number of fronts".

A fuel depot in east-central Ukraine was destroyed on Wednesday in a Russian overnight airstrike, said Valentyn Reznichenko, the head of central Ukraine's Dnipropetrovsk regional military administration.

Also on Wednesday, a car crashed into the gate of the Russian embassy in Bucharest, Romania. According to Russia's TASS news agency, the car subsequently caught fire and the driver died.