Europe must consider stepping up penalties for Moscow by boycotting its gas exports, Germany’s defence minister has said, as foreign outrage mounts over evidence of possible executions and other atrocities by Russian forces in Ukraine.

Japanese prime minister Fumio Kishida said on Monday that “we strongly condemn attacks on civilians”, following reports of bodies found with signs of torture in areas abandoned by Russian forces.

New Zealand prime minister Jacinda Ardern called reports of rape and other atrocities by Russian soldiers “beyond reprehensible”.

Meanwhile, president Volodymyr Zelensky appealed in a video shown Sunday during the Grammy Awards in Las Vegas for musicians and other artists to help tell the story of Russia’s invasion.

“Support us in any way you can,” Mr Zelensky said.

Ukrainian officials said the bodies of 410 civilians were found in towns around the capital, Kyiv, that were recaptured from Russian forces. Mr Zelensky called the killings evidence of genocide.

In Bucha, northwest of the capital, Associated Press journalists saw 21 bodies.

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 shot at close range. At least two had their hands tied behind their backs.

Ukrainian officials blamed Russian soldiers, but Russia’s defence ministry said 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 faced any violent military action and the mayor did not mention any abuses a day after Russian troops left.

Russian president Vladimir Putin’s February 24 invasion has killed thousands of people and forced more than four million Ukrainians to flee their country.

Mr Putin has said the attack is aimed at eliminating a security threat after Ukraine’s government pursued membership in the US-European Nato military alliance.

The head of Ukraine’s delegation in talks with Russia said Moscow’s negotiators informally agreed to most of a draft proposal discussed during talks in Turkey, but no written confirmation has been provided.

Russian demands include Ukraine declaring itself neutral and renouncing membership of military alliances.

Russian forces retreated from some areas around Kyiv after Moscow said it was focusing its offensive on the country’s east, where two regions are controlled by Russian-backed separatists.

Russian troops had rolled into Bucha in the early days of the invasion and stayed until March 30.

The reports of atrocities are severe enough that European officials “would have to talk about halting gas supplies from Russia”, German defence minister Christine Lambrecht said on public broadcaster ARD.

“Such crimes must not go unanswered.”

Europe gets 40% of its gas and 25% of its oil from Russia, while such sales are the Kremlin’s main source of export revenue.

Governments have been scrambling to find ways to reduce that reliance.

Estimates of the impact of a gas boycott on European countries vary but most involve a substantial loss of economic output.

For its part, Russia is temporarily enjoying a windfall as global prices surge due to anxiety over possible supply disruptions.

Kyiv mayor Vitali Klitschko called on countries to end Russian gas imports. He said they were funding the killings.

On Saturday, Lithuania announced it had stopped imports of Russian gas and urged other European governments to do the same.

“If we can do it, the rest of Europe can do it too,” president Gitanas Nauseda said on Twitter, referring to Russia as “the aggressor”.

Some European leaders said the killings in the Kyiv area amounted to war crimes.

US secretary of state Antony Blinken called images of what happened near Kyiv “a punch to the gut”. on CNN’s State of the Union programme. The US has previously said that it believes Russia committed war crimes.

“It is a brutality against civilians we haven’t seen in Europe for decades,” Nato secretary-general Jens Stoltenberg said on the same broadcast.

Russia asked for a meeting on Monday of the UN Security Council to discuss events in the city.

One resident of Bucha, who refused to give his name out of fear for his safety, said Russian troops went from building to building and took people out of the basements where they were hiding.

He said soldiers checked their phones for evidence of anti-Russian activity and took them away or shot them.

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 Mr Zelensky, claimed some of the women had been raped before being killed and the Russians then burned the bodies.

On Monday, the Ukrainian military said its forces had retaken some towns in the Chernihiv region and humanitarian aid was being delivered.

The road between Chernihiv and Kyiv was to reopen to some traffic later in the morning, according to the news agency RBK Ukraina.

The mayor of Chernihiv, which has been cut off from food and other supplies for weeks, said Russian shelling has destroyed 70% of the northern city.

The regional governor in Kharkiv in the northeast said Russian artillery and tanks launched more than 20 strikes on Ukraine’s second-largest city and its outskirts over the past day.

In a video address posted online Sunday, Mr Zelensky 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.

The president directed some of his remarks at the mothers of Russian soldiers.

“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.”

In Motyzhyn, some 30 miles west of Kyiv, residents told AP 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 the mayor was killed while being held by Russian forces.