LONDON: Britain's Defence Ministry says Russia is continuing to build up both its soldiers and mercenaries in eastern Ukraine.
"Russian forces are continuing to consolidate and reorganize as they refocus their offensive into the Donbas region in the east of Ukraine," the ministry said in an intelligence update posted on social media Monday.
It says Russian troops are being moved into the area, along with mercenaries from the Wagner private military group.
Overnight, the U.K. said Russia was still trying to take the southern port city of Mariupol, which has seen weeks of intense fighting.
It said "the city continues to be subject to intense, indiscriminate strikes, but Ukrainian Forces maintain a staunch resistance, retaining control in central areas."
The update added that "Mariupol is almost certainly a key objective of the Russian invasion as it will secure a land corridor from Russia to the occupied territory of Crimea," which it annexed in 2014.
Bodies with bound hands, close-range gunshot wounds and signs of torture lay scattered in a city on the outskirts of Kyiv after Russian soldiers withdrew from the area.
Ukrainian authorities accused the departing forces on Sunday of committing war crimes and leaving behind a "scene from a horror movie."
As images of the bodies emerged from Bucha, European leaders condemned the atrocities and called for tougher sanctions against Moscow.
In a sign of how the horrific reports shook many leaders, Germany's defense minister even suggested that the European Union consider banning Russian gas imports.
Ukrainian officials said the bodies of 410 civilians were found in Kyiv-area towns that were recently retaken from Russian forces.
Associated Press journalists saw the bodies of at least 21 people in various spots around Bucha, northwest of the capital.
One group of nine, all in civilian clothes, were scattered around a site that residents said Russian troops used as a base.
They appeared to have been killed at close range.
At least two had their hands tied behind their backs, one was shot in the head, and another's legs were bound.
Ukrainian officials laid the blame for the killings squarely at the feet of Russian troops, with the president calling them evidence of genocide.
But Russia's Defense Ministry rejected the accusations as "provocation."
The discoveries followed the Russian retreat from the area after Moscow said it was focusing its offensive on the country's east.
Russian troops had rolled into Bucha in the early days of the invasion and stayed up until March 30.
One resident, who refused to give his name out of fear for his safety, said that Russian troops went building to building and took people out of the basements where they were hiding, checking their phones for any evidence of anti-Russian activity before taking them away or shooting them.
Hanna Herega, another resident, said Russian troops started shooting at a neighbor who had gone out to gather wood for heating.
"They hit him a bit above the heel, crushing the bone, and he fell down," Herega said.
"Then they shot off his left leg completely, with the boot. Then they shot him all over."
The AP also saw two bodies, that of a man and a woman, wrapped in plastic that residents said they had covered and placed in a shaft until a proper funeral could be arranged.
"He put his hands up, and they shot him," said the resident who refused to be identified.
Oleksiy Arestovych, an adviser to Ukrainian President Volodymyr Zelenskyy, described bodies lying in suburban streets as a "scene from a horror movie."
He claimed some of the women had been raped before being killed and the Russians then burned the bodies.
In a video address, Zelenskyy said Russian soldiers who killed and tortured civilians were responsible for "concentrated evil."
"It is time to do everything possible to make the war crimes of the Russian military the last manifestation of such evil on earth," he said in remarks translated by his office.
He directed some of his remarks at the mothers of Russian soldiers involved.
"Even if you raised looters, how did they also become butchers?" he said.
"You couldn't overlook that they are deprived of everything human. No soul. No heart. They killed deliberately and with pleasure."
Zelenskyy said his government would take steps to create a special justice mechanism to investigate every crime committed by the Russian forces in Ukraine.
Zelenskyy also appeared in a video message at Sunday's Grammy Awards, contrasting the lives of those attending the award ceremony in Las Vegas with the lives of musicians in his battered homeland.
"Our musicians wear body armor instead of tuxedos. They sing to the wounded in hospitals, even to those who can't hear them," he said.
"But the music will break through anyway."
Russia's Defense Ministry said in a statement that photos and videos of dead bodies "have been stage managed by the Kyiv regime for the Western media."
The ministry said "not a single civilian" in Bucha had faced any violent military action and the mayor did not mention any abuses a day after Russian troops left.
Russia asked for a meeting Monday of the U.N. Security Council to discuss events in the city.
The U.S. and Britain have recently accused Russia of using Security Council meetings to spread disinformation.
In Motyzhyn, some 50 kilometers (30 miles) west of Kyiv, residents told AP on Sunday that Russian troops killed the town's mayor, her husband and her son and threw their bodies into a pit in a pine forest behind houses where Russian forces had slept.
Inside the pit, AP journalists saw four bodies of people who appeared to have been shot at close range.
The mayor's husband had his hands behind his back, with a piece of rope nearby, and a piece of plastic wrapped around his eyes like a blindfold.
Ukrainian Deputy Prime Minister Iryna Vereshchuk confirmed that the mayor was killed while being held by Russian forces.
Some European leaders said the killings in the Kyiv area amounted to war crimes.
The U.S. has previously said that it believes Russia has committed war crimes, and Secretary of State Anthony Blinken called images of what happened near Kyiv "a punch to the gut" on CNN's "State of the Union."
"It is a brutality against civilians we haven't seen in Europe for decades," NATO Secretary-General Jens Stoltenberg said on the same show.
Kyiv Mayor Vitali Klitschko called on nations to immediately end Russian gas imports, saying they were funding the killings.
In a turnaround, Germany's defense minister said that the EU should consider doing just that.
Ministers "would have to talk about halting gas supplies from Russia," Defense Minister Christine Lambrecht said Sunday night on German public broadcaster ARD.
"Such crimes must not go unanswered."
Russia provides 40% of Europe's gas and 25% of its oil, and until now many EU nations have resisted calls to scale back or fully end reliance on Russian fossil fuels.
Giving them up would mean even higher prices at the pump and higher utility bills, potentially creating an energy crisis and a recession.
The U.S. has previously announced a ban on Russian oil, but it imports only a small share of Russia's oil exports and doesn't buy any of its natural gas.
As Russian forces retreated from the area around the capital, they also withdrew from the Sumy region, in Ukraine's northeast, local administrator Dmitry Zhivitsky said in a video message carried by Ukrainian news agencies Sunday.
The troops had occupied the area for nearly a month.
They pressed their sieges in other parts of the country.
Russia has said it is directing troops to the Donbas in eastern Ukraine, where Russia-backed separatists have been fighting Ukrainian forces for eight years.
In that region, Mariupol, a port on the Sea of Azov that has seen some of the war's greatest suffering, remained cut off.
About 100,000 civilians, less than a quarter of the prewar population of 430,000, are believed to be trapped there with little or no food, water, fuel and medicine.
The International Committee of the Red Cross said Sunday that a team sent Saturday to help evacuate residents had yet to reach the city.
Ukrainian authorities said Russia agreed days ago to allow safe passage from the city, but similar agreements have broken down repeatedly under continued shelling.
The mayor of Chernihiv, which has also been cut off from shipments of food and other supplies for weeks, said that relentless Russian shelling has destroyed 70% of the northern city.
The Ukrainian military said early Monday that its forces had retaken some towns in the Chernihiv region and that humanitarian aid was being delivered.
The road between Chernihiv and the capital, Kyiv, was to reopen to some traffic later in the morning, according to the news agency RBK Ukraina.
The regional governor in Kharkiv said Sunday that Russian artillery and tanks launched over 20 strikes on Ukraine's second-largest city and its outskirts in the country's northeast over the past day.
The head of Ukraine's delegation in talks with Russia said Moscow's negotiators informally agreed to most of a draft proposal discussed during face-to-face talks in Istanbul this week, but no written confirmation has been provided.
The Russian invasion has left left thousands dead and forced more than 4 million Ukrainians to flee their country.
(With AP Inputs)