Ukraine said Saturday Russian forces were making a "rapid retreat" from around the capital Kyiv and the city of Chernigiv, as evidence emerged of possible civilian killings in areas they have been occupying.

AFP reporters saw at least 20 bodies on a single street in the town of Bucha near Kyiv, including one with his hands tied, and the body of a missing photographer was discovered in a nearby village.

Ukrainian servicemen survey the area from their position along the front line, north of the Ukrainian capital of Kyiv on March 31, 2022
Ukrainian servicemen survey the area from their position along the front line, north of the Ukrainian capital of Kyiv on March 31, 2022 AFP / Sergei SUPINSKY

"All these people were shot," Bucha's mayor Anatoly Fedoruk told AFP, adding that 280 other bodies had been buried in mass graves in the town.

As it withdraws from northern areas, Russia appears to be focusing on the east and south of Ukraine, where it already hold vast swathes of territory.

"Russia is prioritising a different tactic: falling back on the east and south," Ukrainian presidential adviser Mykhaylo Podolyak said on social media.

Position of Russian forces in and around Mariupol on March 9, 16, 23 and 30.
Position of Russian forces in and around Mariupol on March 9, 16, 23 and 30. AFP / Kenan AUGEARD

"Without heavy weapons we won't be able to drive (Russia) out," he said.

President Vladimir Putin ordered tanks into Russia's pro-Western neighbour on February 24 and Ukraine estimates 20,000 people have been killed in the war so far.

A teddy bear is pictured in a destroyed house in the outskirts of Kyiv, on March 31, 2022, amid Russian invasion of Ukraine
A teddy bear is pictured in a destroyed house in the outskirts of Kyiv, on March 31, 2022, amid Russian invasion of Ukraine AFP / RONALDO SCHEMIDT

More than 10 million have had to flee their homes.

Pope Francis spoke of "icy winds of war" again sweeping over Europe as he brought up the conflict at the outset of his trip to Malta on Saturday.

"Once again, some potentate, sadly caught up in anachronistic claims of nationalist interests, is provoking and fomenting conflicts," the pope said.

A Ukrainian serviceman holds an assault rifle in a trench at the front line east of Kharkiv on March 31, 2022
A Ukrainian serviceman holds an assault rifle in a trench at the front line east of Kharkiv on March 31, 2022 AFP / FADEL SENNA

A visit to the Ukrainian capital was "still on the table," he added.

A Ukrainian serviceman smokes a cigarette in a trench at the front line east of Kharkiv on March 31, 2022
A Ukrainian serviceman smokes a cigarette in a trench at the front line east of Kharkiv on March 31, 2022 AFP / FADEL SENNA

Ukrainian authorities on Saturday said the body of a well-known photographer, Maks Levin, had been found near a village in the region around Kyiv that had been caught up in the fighting.

"According to preliminary information, unarmed Maxim Levin was killed by servicemen of the Russian Armed Forces with two shots from small fire arms," prosecutors said in a statement on Telegram.

A Ukranian soldier stands on the cannon of a burnt Russian tank on the outskirts of Kyiv, on March 31, 2022
A Ukranian soldier stands on the cannon of a burnt Russian tank on the outskirts of Kyiv, on March 31, 2022 AFP / RONALDO SCHEMIDT

Levin, a 40-year-old father of four, had been reported missing on March 13 and the body was found near Guta Mezhygirksa on April 1, officials said.

The NGO Reporters Without Borders said Levin was the sixth journalist killed in the conflict.

In Bucha, 16 of the 20 corpses found on one street were lying either on the pavement or by the verge. Three were sprawled in the middle of the road, and another lay on his side in the courtyard of a destroyed house.

Ukrainian soldiers stand by a burnt Russian tank on the outskirts of Kyiv, on March 31, 2022
Ukrainian soldiers stand by a burnt Russian tank on the outskirts of Kyiv, on March 31, 2022 AFP / RONALDO SCHEMIDT

An open Ukrainian passport lay on the ground next to the person who had his hands tied behind his back with a piece of white cloth. Two other people had white cloth tied around their upper arms.

All were wearing civilian clothes -- winter coats, jackets or tracksuit tops, jeans or jogging bottoms, and trainers or boots.

The International Criminal Court has already opened a probe into possible war crimes committed in Ukraine and several Western leaders, including US President Joe Biden, have accused Putin of being a "war criminal".

Russia's efforts to consolidate its hold on southern and eastern areas of the country have been hampered by the resistance of Mariupol despite devastating attacks lasting weeks.

At least 5,000 residents have been killed, according to local officials.

The estimated 160,000 who remain face shortages of food, water and electricity.

Dozens of buses carrying Mariupol residents who had escaped the city earlier arrived on Friday in Zaporizhzhia, 200 kilometres (120 miles) to the northwest.

The buses brought people who had been able to flee Mariupol to Russian-occupied Berdiansk.

"My house was destroyed. I saw it in photos. Our city doesn't exist anymore," said Olena, who carried her young daughter in her arms.

The International Committee of the Red Cross (ICRC) said its team headed to Mariupol to try and conduct an evacuation but was forced to turn back Friday.

The ICRC said its team left again on Saturday bound for Mariupol to make another attempt.

"They are spending the night en route to Mariupol and are yet to reach the city," an ICRC spokesperson said.

In another city in the south, Enerhodar, which is under Russian control, a Ukrainian official said Russian forces opened fire on peaceful demonstrators, injuring four with "severe burns".

Russian troops took control of Enerhodar, the site of Europe's largest nuclear power plant, in early March.

"The occupiers used light and noise grenades and opened mortar fire on the residents, four people were injured and severely burned," she said.