Kyiv (Ukraine) (AFP) - Ukraine said it had regained control of the Kyiv region, with Russian troops retreating from around the capital and Chernigiv city, as evidence emerged of civilian killings in areas the invading forces have been occupying.

AFP reporters saw at least 20 bodies, all in civilian clothing, strewn across a single street in the town of Bucha near the capital and the body of a missing photographer was discovered in a nearby village.

Three of them were tangled up in bicycles after taking their final ride, while others had fallen next to bullet-ridden and crushed cars.

One had his hands tied behind his back with a white cloth, and his Ukrainian passport left open beside his corpse, said AFP journalists who accessed the ravaged town.

"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.

"These are the consequences of Russian occupation," said Fedoruk.

British Foreign Secretary Liz Truss said she was "appalled by atrocities in Bucha and other towns in Ukraine".

"Reports of Russian forces targeting innocent civilians are abhorrent. The UK is working with others to collect evidence and support @IntlCrimCourt war crimes investigation. Those responsible will be held to account," Truss tweeted late Saturday.

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

President Volodymyr Zelensky has also accused Russian soldiers of planting mines and other booby traps as they withdraw from northern Ukraine.

"They are leaving behind a complete disaster and many dangers.... Firstly, the air strikes may continue. Secondly, they are mining the whole territory. Mining houses, equipment, even the bodies of people who were killed," he said in a video address Saturday, warning returning residents of tripwires and other dangers.

"We are moving forward. Moving carefully and everyone who returns to this area must also be very careful," he said.

While Russian forces appeared to be withdrawing from the north, a series of explosions were heard Sunday morning in the historic Black Sea port of Odessa, with an AFP journalist reporting columns of black smoke and flames visible, apparently in an industrial part of the strategic city.

Anton Herashchenko, adviser to the interior minister, said Odessa was attacked from the air.

"Fires were reported in some areas. Part of the missiles were shot down by air defence," he wrote on Telegram.

Meanwhile, in an attempt to raise economic pressure on Russia, the Baltic states of Latvia, Estonia and Lithuania announced Saturday that they had stopped all imports of Russian natural gas.

'Verbal Agreement' From Russia

In a potential sign of progress to end the fighting, Ukrainian negotiator David Arakhamia told local television channels that Russia had "verbally" accepted most of Kyiv's proposals in peace talks -- except on the issue of Crimea, which Moscow annexed in 2014.

Among the agreed-upon points was that a referendum on Ukraine's neutral status "will be the only way out of this situation", Arakhamia said.

He said any meeting between Zelensky and Putin would "with a high probability" take place in Turkey, which has sought to mediate the conflict.

As Russian forces withdraw from some northern areas, Moscow appears to be focusing on eastern and southern Ukraine, where it already holds vast swathes of territory.

"What is the aim of the Russian forces? They want to seize both Donbas and the south of Ukraine," Zelensky said in a video address late Saturday. "What is our goal? To defend our freedom, our land, and our people."

But Ukrainian presidential adviser Mykhaylo Podolyak warned on social media that "without heavy weapons we won't be able to drive (Russia) out".

Ukraine authorities nevertheless offered citizens elements of good news Saturday in claiming progress against the Russians more than five weeks after Moscow's invasion triggered Europe's worst conflict in decades.

"Irpin, Bucha, Gostomel and the whole Kyiv region were liberated from the invader," deputy defence minister Ganna Maliar said on Facebook, referring to towns that have been heavily damaged or destroyed by fighting.

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.

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 Saturday at the outset of his trip to Malta -- and made what appeared to be a barely veiled reference to Putin.

"Once again, some potentate, sadly caught up in anachronistic claims of nationalist interests, is provoking and fomenting conflicts," the pope said, adding he was still considering a visit to Ukraine's capital.

Journalist Killed With 'Two Shots'

Ukrainian authorities said Saturday 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. Levin became the sixth journalist killed in the war, according to Reporters Without Borders.

Prosecutors said Levin, who was unarmed, "was killed by servicemen of the Russian Armed Forces with two shots from small-fire arms".

Levin, a 40-year-old father of four, had been reported missing on March 13; his body was found on April 1.

In Russia, hundreds of people gathered across the country Saturday to protest against the war in Ukraine. Police detained 211 people in several cities, including more than 20 people in a Moscow park under heavy snowfall, according to OVD-Info, a group that monitors arrests.

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

At least 5,000 residents have been killed in the besieged southern port city, according to local officials, while the estimated 160,000 who remain face shortages of food, water and electricity.

The International Committee of the Red Cross (ICRC) said its team left for Mariupol on Saturday to make another attempt at conducting an evacuation, after being forced to turn back the day before.

In another southern city, Enerhodar, which is under Russian control, a Ukrainian official said Russian forces opened fire on peaceful demonstrators, injuring four.

In a video address, Zelensky thanked the residents of Enerhodar, the site of Europe's largest nuclear power plant, which had been seized by Russian troops in early March, for their bravery.

"When people protest, and the more they protest, the harder it is for the occupiers to destroy us, to destroy our freedom," Zelensky said.