Russian forces were in retreat in the country's north in fronts near the the capital Kyiv and the city of Chernihiv, Ukrainian authorities said Saturday as the besieged country's forces reestablish control in areas west of Dnieper River and regain various towns and villages.

Russian forces now appear to be focusing attacks in the east and south, a day after thousands of people from the besieged southern port city of Mariupol and surrounding Russian-held areas escaped in a convoy of buses and private cars organized by the Red Cross.

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

He said that, while Russian forces appeared to be pulling back from Kyiv and Chernihiv, their aim was to "control a vast stretch of occupied territory and set up there in a powerful way."

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

Ukraine has regained control of "the whole Kyiv region" after invading Russian forces retreated from some key towns, Deputy Defense Minister Ganna Maliar said on Saturday.

"Irpin, Bucha, Hostomel and the whole Kyiv region were liberated from the invader," Maliar said on Facebook, referring to towns that have been heavily destroyed by fighting. Irpin and Bucha, commuters towns outside Kyiv, were retaken by the Ukrainian army this week.

Hostomel, near Kyiv, was the setting of heavy fighting to take control of an airfield, while both Irpin and Bucha have suffered vast destruction and large civilian death tolls.

President Vladimir Putin ordered Russian troops into Ukraine on Feb. 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.

Zelenskyy warns of mines, traps laid by retreating Russians

As Russian forces pull back from Ukraine’s capital region, retreating troops are creating a "catastrophic" situation for civilians by leaving mines around homes, abandoned equipment and "even the bodies of those killed," President Volodymyr Zelenskyy warned Saturday.

Ukraine and its Western allies reported mounting evidence of Russia withdrawing its forces from around Kyiv and building its troop strength in eastern Ukraine. Ukrainian fighters reclaimed several areas near the capital after forcing the Russians out or moving in after them, officials said.

The visible shift did not mean the country faced a reprieve from more than five weeks of war or that the more than 4 million refugees who have fled Ukraine will return soon. Zelenskyy said he expects departed towns to endure missile strikes and rocket strikes from afar and for the battle in the east to be intense.

"It’s still not possible to return to normal life, as it used to be, even at the territories that we are taking back after the fighting. We need wait until our land is demined, wait till we are able to assure you that there won’t be new shelling," the president said during his nightly video address, though his claims about Russian mines couldn't be independently verified.

On the outskirts of Kyiv, signs of fierce fighting were everywhere in the wake of the Russian redeployment. Destroyed armored vehicles from both armies left in streets and fields and scattered military gear covered the ground next to an abandoned Russian tank.

Ukrainian forces recaptured the city of Brovary, 20 kilometers (12.4 miles) east of the capital, Mayor Ihor Sapozhko said in a televised Friday night address. Shops were reopening and residents were returning but "still stand ready to defend" their city, he added.

"Russian occupants have now left practically all of the Brovary district," Sapozhko said. "Tonight, (Ukrainian) armed forces will work to clear settlements of (remaining) occupants, military hardware and possibly from mines."

Mass grave, civilian bodies in Bucha

Bucha's mayor said 280 people had been buried in a mass grave in Bucha and that the town is littered with corpses.

The bodies of at least 20 men in civilian clothes were found lying in a single street Saturday after Ukrainian forces retook the town of Bucha near Kyiv from Russian troops, Agence France-Presse (AFP) journalists said.

One of the bodies of the men had his hands tied, and the corpses were strewn over several hundred meters of the residential road in the suburban town northwest of the capital.

The cause of death was not immediately clear although at least one person had what appeared to be a large head wound.

Russian forces withdrew from several towns near Kyiv in recent days after Moscow's bid to encircle the capital failed, with Ukraine declaring that Bucha had been "liberated."

But the town had been left devastated by the fighting, with gaping holes from shell explosions in apartment blocks and crushed cars littering the streets, AFP journalists who accessed the town said.

Sixteen of the 20 corpses found on one street in Bucha were lying either on the pavement or by the verge. Three were sprawled in the middle of the road and another was lying in the courtyard of a house.

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.

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

Two of them lay near bicycles while another was next to an abandoned car. Some lay face up, with their limbs askew, while others were lying face down.

The skin on the faces of the dead people had taken on a pale waxy appearance, indicating that they may have been there for at least a number of days.

The Ukrainian soldiers, backed by a column of tanks and armored vehicles, attached cables to the bodies and pulled them off the street, fearing they may be booby-trapped with explosive devices, the Associated Press (AP) reported.

As they moved on the streets of Bucha, the Ukrainian soldiers cleared barricades and inspected suspicious objects. They placed red rags on remnants of unexploded ordnance to draw attention to the possibility of explosions.

Residents of the town said the civilians were killed by Russian soldiers without apparent provocation.

"Those people were just walking and they shot them without any reason. Bang," said a Bucha resident who declined to give his name, citing safety reasons. "In the next neighbourhood, Stekolka, it was even worse. They would shoot without asking any question."

Authorities have said that at least 200 people have been killed in Irpin, a suburb of Kyiv, since Russia invaded Ukraine in late February.

Journalist Levin found dead near Kyiv

In Kyiv, the government confirmed that the body of a well-known photographer, Maks Levin, had been found near a village in the region around the capital 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.

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

The NGO Reporters Without Borders (RSF) said six journalists have been killed in the conflict so far, adding: "Targeting journalists is a war crime."

The International Criminal Court (ICC) has already opened a probe into possible war crimes in Ukraine. Former war crimes prosecutor Carla Del Ponte said in an interview published on Saturday that the ICC should issue an arrest warrant for Putin.