MUKACHEVO, Ukraine — Ukrainian troops recaptured territory around Kyiv on Saturday as Russian forces pulled back from towns they had seized in the opening days of the war and left in their wake scenes of destruction and horror, including the abandoned bodies of dead civilians.

Journalists entered the town of Bucha, a suburb northwest of the capital, and saw numerous corpses strewn on the streets. Video posted to social media and verified by The Washington Post showed what appeared to be at least nine dead, including one child.

Bucha’s mayor, Anatoly Fedoruk, said in an interview that around 270 local residents had been buried in two mass graves. He estimated that 40 people were lying dead in the streets. Some had been bound and executed — shot in the back of the head, he said.

The mayor added that officials are worried that the bodies could be booby-trapped with explosives. In a video address to Ukrainians early Saturday, Ukrainian President Volodymyr Zelensky said Russia was “mining the whole territory.”

“They are mining homes, mining equipment, even the bodies of people who were killed,” he said. The Post has not verified those claims.

Revelations of atrocities and alleged war crimes, including reports of soldiers firing on civilian protesters in the east, cast a pall over what has in some ways been a hopeful period for Ukrainians as they resist the Russian invaders.

The capital appears safe for the moment, but at the same time, shelling and intense fighting in the east and south of the country are continuing. Efforts to rescue civilians in besieged cities have been slowed by the extremely dangerous conditions on the ground.

The war, in its 38th day, remained a grinding conflict with no clear resolution in sight. The Russian strategic pivot may foreshadow a long war of attrition. That would prolong the already severe humanitarian crisis in which millions of Ukrainians have fled their homes, becoming refugees in neighboring countries.

A cease-fire in the largely destroyed coastal city of Mariupol has been in place for several days, creating a corridor to leave the city. A team from the Red Cross failed to reach the city Friday or Saturday, citing the unsafe environment. A Red Cross spokesperson emailed a note with few details saying that teams are en route but have yet to reach Mariupol.

Western military analysts are still trying to interpret the decision by Russian military commanders to reposition their forces. Russian officials have said they are concentrating their forces in the eastern part of the country. The repositioning could signal an intense battle for control of the Donbas region. It appears that, at least for now, Russian President Vladimir Putin has recalculated what he can and can’t achieve with his invasion of Ukraine.

Ukraine’s deputy defense minister, Anna Malyar, said late Saturday that the entire Kyiv administrative region is fully under Ukrainian control.

Zelensky had said earlier that the movement of Russian forces was “slow but noticeable.”

But he continued his ongoing appeal to allied nations to do more to aid his war-scorched country. He cited the suffering in Mariupol, where tens of thousands of residents have been trying to survive amid the rubble.

“Europe has no right to react in silence to what is happening in our Mariupol. The whole world must react to this humanitarian catastrophe,” Zelensky said in his video address.

Zelensky’s demand for help came amid significant battlefield developments that potentially could alter the geography of the war.

If, as some Western analysts believe, Putin focuses on expanding his control of territory in the east, it would open a broad corridor between Russia and the Crimean peninsula annexed by Russia in 2014. But a more limited strategic goal could undermine support within Russia for the war effort.

But after Moscow’s negotiators agreed in talks with Ukraine to de-escalate the fighting around Kyiv and Chernihiv, and focus instead on the eastern Donbas region, propagandists and pro-war politicians expressed dismay. Prominent state television anchor Vladimir Solovyov said Thursday that “that any negotiation with the Nazis until the boot is on their throat is weakness. You shouldn’t shake hands with this creep,” he said, apparently referring to Zelensky.

Another pro-Kremlin journalist and blogger Semyon Pegov, from the outlet War Gonzo, which reports from the Russian side of the war, said the invasion was just beginning and that Russia would continue “to the end.” He called Russian soldiers “real Russian heroes.”

“No one and nothing will take away their feat from them,” he posted to Telegram on Friday. “It’s already gone down in history.”

As part of their retreat, Russian forces abandoned an airport seized at the start of the invasion. Near the border with Belarus, Ukrainian forces regained control of the disabled Chernobyl nuclear power plant that had been attacked and captured by Russian forces. The national flag once again was raised over the plant.

The repositioning of troops so far has been relatively modest and is possibly a tactic to fool the Ukrainians into lowering their defensive posture in the capital, Brookings Institution defense analyst Michael O’Hanlon said Saturday. He added the Russians may be hoping that Zelensky reveals his whereabouts.

“If they can get the Ukrainians to lower their guard, that would be for them potentially an opportunity to make a strike against Zelensky and/or his inner circle and the top tier of the government,” O’Hanlon said. “I still think there’s a possibility that they’re trying to lure the Ukrainians into making a mistake.”

On-and-off negotiations for a broad cease-fire have been on again in recent days, but the sincerity of the Russians at the table has been questioned by their Ukrainian counterparts. They fear, as do security analysts in the West, that Russian gestures toward a cease-fire and a negotiated peace could be a diversion to help the attackers reposition their forces after the initial thrust of the invasion yielded disappointing results.

According to Ukrainian media reports, David Arakhamia, the head of the Ukrainian delegation to the talks, said officials are preparing for a possible meeting between Zelensky and Putin in Turkey.

Ukrainian presidential adviser Oleksiy Arestovych told national television that Ukrainians should prepare for “difficult fights” ahead in Mariupol and in the southern and eastern regions of the country.

In the east, four people were “injured and severely burned” after Russian forces fired mortars at protesters in a city near Zaporizhzhia, the site of a nuclear plant that Russia captured last month, according to Ukraine’s human rights ombudswoman.

Residents of Enerhodar, a satellite town of Zaporizhzhia, which has been occupied by Russian forces for nearly four weeks, held a rally in support of Ukraine on Saturday. Russian soldiers used light and noise grenades to disrupt the protest and opened mortar fire on residents, the ombudswoman, Lyudmyla Denisova, said in a statement posted to Telegram.

“Such treatment of civilians is a crime against humanity and a war crime as defined by the Rome Statute of the International Criminal Court,” Denisova said.

The Washington Post verified two videos recorded by witnesses and posted to Telegram. The images were filmed at the same time from separate angles and show at least nine flashes followed by large booms. Gunfire is audible as people run away from the site of the protest.

“There is a fight in the city center!” a man yells in a third video, verified by The Post, while rushing away from multiple loud booms. “Russian occupiers attacked civilians. There was a peaceful protest here.”

Tens of thousands of people in recent weeks have fled Ukrainian cities under attack by Russian forces after Kyiv and Moscow agreed on fragile evacuation deals.

Across Ukraine, seven humanitarian corridors have been established, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk, including the one from Mariupol. She said in a Telegram post that more than 6,000 people were evacuated from front-line cities to other parts of the country on Friday.

Vereshchuk said those evacuees included more than 1,400 people who left in their vehicles along planned routes from the southern cities of Berdyansk and Melitopol, which are under Russian control, to the nearby Zaporizhzhia region.

Among them were hundreds of people from Mariupol who had managed to escape in private vehicles. Separately, she said, a convoy of 42 buses carried Mariupol residents to Zaporizhzhia from Berdyansk, which they had previously reached on their own.

In southern Ukraine, the death toll from a missile strike that hit a main government building in the city of Mykolaiv this week has risen to 32, the governor of the region, Vitaliy Kim, said Saturday on Telegram.

Dozens of people remain unaccounted for after that attack blasted a hole through part of the building, Dmytro Pletenchuk, a press officer of the Mykolaiv Regional State Administration, said earlier. More than 30 people were injured, he said as rescue workers continued to clear rubble Friday and funerals were held for many of the victims.

The war continues to stir tensions globally and could have ramifications in low Earth orbit: The director of Russia’s space agency suggested he would submit a proposal to end his country’s cooperation in the International Space Station program.

In tweets on Saturday, Dmitry Rogozin, head of the agency Roscosmos, pointed to sanctions against a “number of enterprises in the Russian rocket and space industry.” He said that he appealed to the heads of NASA, the Canadian Space Agency and the European Space Agency to lift sanctions and that in their responses, the “position of our partners is clear: the sanctions will not be lifted.”

“I believe that the restoration of normal relations between partners in the International Space Station and other joint projects is possible only with the complete and unconditional lifting of illegal sanctions,” Rogozin wrote.

Rogozin has frequently used threatening and blustery rhetoric, including to repeatedly suggest Russia could exit the partnership. His latest remarks came three days after two Russian cosmonauts and a NASA astronaut returned from the space station, a symbol of partnership in space even amid mounting tensions over the war in Ukraine.

Since Russian forces invaded Ukraine on Feb. 24, NASA has maintained that the station has been operating as normal, unaffected by the conflict. NASA has said it would be unable to operate the space station without the Russians because the nation provides the propulsion necessary to keep the station in orbit.

In China, officials on Saturday renewed their criticism of sanctions placed on Russia. The remarks came a day after a high-level virtual summit between China and the European Union.

“We oppose sanctions, and the effects of these sanctions also risk spilling to the rest of the world,” Wang Lutong, director general of European affairs at China’s Foreign Ministry, told reporters on Saturday.

Since Russian forces invaded Ukraine, E.U. leaders have taken a tougher stance on China, urging it to drop its tacit support for the invasion and work for peace — but Beijing is pushing back.

“China is not a related party on the crisis of Ukraine. We don’t think our normal trade with any other country should be affected,” Wang said. He added that China is contributing to the global economy by conducting normal trade with Russia.

Pope Francis said Saturday that he is considering making a trip to Kyiv. While traveling from Rome to Malta, the leader of the Roman Catholic Church was asked by a reporter on his plane whether a visit to Ukraine was a possibility following invitations from Ukrainian political and religious officials.

“Yes, it is on the table,” Francis answered, but he offered no further details, according to Reuters.

Zelensky has spoken twice with the pope by telephone, according to the Vatican, and along with Kyiv Mayor Vitali Klitschko has extended invitations to Francis to visit Ukraine. The country has a sizable Roman Catholic population. However, most Ukrainian Catholics identify with the Ukrainian Greek Catholic Church.

Francis has vocally condemned the war in Ukraine, calling it a “senseless massacre where every day slaughters and atrocities are being repeated.”

Achenbach reported from Washington; Dixon reported from Riga, Latvia; and Suliman reported from London. Dalton Bennett in Dnipro, Ukraine; Isabelle Khurshudyan in Odessa, Ukraine; Liz Sly and Ellen Francis in London; Amy Cheng and Andrew Jeong in Seoul; and Claire Parker, Meg Kelly, Frances Stead Sellers, Paulina Firozi, Lateshia Beachum, Christian Davenport and Zachary Nelson in Washington contributed to this report.