A Russian soldier in a theatre in Mariupol, which has could soon fall to Moscow

Kramatorsk (Ukraine) (AFP) - US President Joe Biden accused Vladimir Putin of committing genocide against civilians in Ukraine, as Kyiv halted humanitarian corridors in several parts of the country Wednesday deemed “too dangerous” for evacuations.

Biden’s accusation came as Moscow – already accused by the West of widespread atrocities against civilians – appears to be readying a massive offensive across Ukraine’s eastern Donbas region that Washington warned might involve chemical weapons.

In Mariupol, where strikes continued to pummel the battered city, more than 1,000 Ukrainian soldiers have surrendered, Russia’s defence ministry said Wednesday. Ukraine did not confirmed the claim.

Following its pullback from areas north of Ukraine’s capital, Kyiv, Russia is refocusing its efforts eastward, the new frontline of the nearly seven-week war.

It appears aimed at capturing more territory in Donbas, where Russian-backed separatists control the Donetsk and Lugansk regions, to create a solid southern corridor to occupied Crimea.

Ukrainian authorities have been urging people to flee west in advance of the expected Russian offensive but on Wednesday, all humanitarian corridors were halted, Deputy Prime Minister Iryna Vereshchuk said.

“The situation along the routes is too dangerous,” Vereshchuk said, claiming Russian forces around Zaporizhzhia in the south were blocking buses transporting the evacuated, while shooting at fleeing civilians in Lugansk.

Russian offensive imminent in Donbas

In the past 24 hours, seven civilians were killed by Russian shelling in the northeastern Kharkiv region, said regional governor Oleg Synegubov on social media.

Biden’s charge of genocide was the strongest accusation yet from Washington against Putin, yet one that Ukrainian President Volodymyr Zelensky has repeatedly levelled.

Biden previously called Putin a “war criminal” following the discovery of hundreds of civilians killed in Bucha and neighbouring Kyiv suburbs held by Russian forces that sparked global condemnation.

“Yes, I called it genocide,” said Biden, defending his use of the term Tuesday during a speech, while saying he’d let lawyers decide “whether or not it qualifies” as such.

“It’s become clearer and clearer that Putin is just trying to wipe out the idea of even being able to be a Ukrainian.”

US President Joe Biden has for the first time accused Vladimir Putin's forces of committing genocide in Ukraine

The International Criminal Court’s chief prosecutor Karim Khan said Wednesday that “Ukraine is a crime scene”, speaking on a visit to Bucha.

“We’re here because we have reasonable grounds to believe that crimes within the jurisdiction of the court are being committed. We have to pierce the fog of war to get to the truth,” he told reporters.

- Clean them out -

The worst civilian toll is feared to be in Mariupol, where Zelensky accuses Russia of killing “tens of thousands”.

On Wednesday, the Ukrainian army said on Telegram that air strikes continued, particularly targeting its port and the huge Azovstal iron and steel works.

The heaviest civilian toll is feared to be in Mariupol, where Zelensky said he believed Russia had killed 'tens of thousands'

The maze-like complex has been a focus of resistance in Mariupol, with fighters using a tunnel system below the vast industrial site to slow Russian forces down.

“It’s a city within a city,” said Eduard Basurin, a representative for pro-Russian separatists in Donetsk, citing subterranean areas that cannot be bombed from above.

“You have to go underground to clean them out, and that will take time.”

US Secretary of State Antony Blinken said he could not confirm allegations that Russia had used chemical weapons in the area, but Washington had “credible information” Russia might use tear gas mixed with chemical agents in the besieged port.

- ‘Devil incarnate’ -

On Wednesday, US private satellite firm Maxar Technologies published images it said showed ground forces moving towards Russia’s border with Ukraine on Monday, likely in preparation for an offensive.

This satellite image released by Maxar Technologies shows a convoy of military vehicles near Bilokurakyne, Ukraine

In the eastern city of Kramatorsk, the Ukrainian military’s main operations hub for the region, a steady stream of residents sought once again to leave by bus and train

The city’s train station was hit by a missile attack on Friday that killed 57 people.

“What is happening is inhuman, (Putin) is a fascist. I don’t know what to call him – a devil incarnate,” said Russian-born Valentina Oleynikova, 82, fleeing the city with her husband.

Another woman, 44-year-old Nadiya Zhizhunas, bid goodbye to her husband, holding him tightly for several minutes before boarding a train.

“I have no idea when we will be together again,” Zhizhunas said. “We have to survive first.”

- ‘No words’ -

In areas recently abandoned by Russian forces, the grim work of accounting for the civilian dead continued.

In the Kyiv commuter town of Gostomel, north of Bucha, locals exhumed the body of Mayor Yuriy Prylypko, whom authorities said was shot while “handing out bread to the hungry and medicine to the sick” and hastily buried by a local priest.

Up to 400 people are unaccounted for Gostomel, said regional prosecutor Andiy Tkach, as war crimes investigators began a probe. AFP witnessed dozens of body bags filling a refrigerated lorry trailer, as two others awaited more corpses.

Loading the truck, Igor Karpishen said he had never before done such work.

“But our citizens are murdered and we must bury every person in the right way,” said Karpishen.

“I don’t have any words to express these feelings.”

Zelensky sounded the alarm Tuesday about snowballing allegations of rape and sexual assault by Russian forces in previously held areas, saying hundreds of cases had been recorded, including of young children and a baby.

Bucha Mayor Anatoly Fedoruk said more than 400 people were found dead after Moscow’s forces withdrew, with 25 reported rapes.

Putin dismissed reports of civilian atrocities as “fakes” Tuesday while saying the Russian offensive was proceeding according to plan.

Meanwhile, an official in the central Ukrainian city of Dnipro said Wednesday that the remains of more than 1,500 Russian soldiers were being kept in its morgues.

- Tycoon swap -

The presidents of Poland, Estonia, Lithuania and Latvia headed for Kyiv in a show of support Wednesday, a day after Germany’s President Frank-Walter Steinmeier – who has long held a detente policy towards Moscow – said his offer to visit was rejected.

In a separate development, Zelensky offered to swap a pro-Kremlin tycoon – arrested after escaping from house arrest – for captured Ukrainians.

Zelensky posted a picture of a handcuffed Viktor Medvedchuk – one of Ukraine’s richest people, who counts Putin among his personal friends – wearing a Ukrainian army uniform.

Medvedchuk, a hugely controversial figure in Ukraine, was under house arrest over accusations of attempting to steal natural resources from Russia-annexed Crimea and of handing Ukrainian military secrets to Moscow.