The discovery of dozens of bodies, some with their hands bound, in a number of towns near the Ukrainian capital of Kyiv after Russian troops retreated from the territories has sparked international outrage.

Ukraine has accused Russia of carrying out the killings in towns near Kyiv, including in Bucha, Irpin and Hostomel, with President Volodymyr Zelenskyy branding Russian forces as "murderers, torturers and rapists" who were committing "genocide" in his country.

Ukrainian officials said the bodies of 410 civilians were found in towns around the capital that were recaptured from Russian forces. In Bucha, northwest of the capital, Associated Press (AP) 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.

As foreign outrage mounts over evidence of possible executions and other atrocities by Russian forces in Ukraine, German Minister of Defense Christine Lambrecht said Europe must consider stepping up penalties for Moscow by boycotting its gas exports, an economically painful step European leaders previously avoided.

The calls were echoed by French President Emmanuel Macron, who argued on Monday that a new round of sanctions targeting Russia was needed and that there were clear indications Russian forces were responsible for the killings of civilians in the Ukrainian town of Bucha.

"There are very clear clues pointing to war crimes. It is more or less established that the Russian army is responsible (for the Bucha killings)," Macron told France Inter radio. "What happened in Bucha demands a new round of sanctions and very clear measures," Macron added.

Those new sanctions should target coal and oil, said Macron, who faces a reelection battle this month.

Japanese Prime Minister Fumio Kishida said 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."

Polish Prime Minister Mateusz Morawiecki on Monday called for an international investigation into what he termed a "genocide" carried out by Russian troops in Ukraine, including in the town of Bucha.

"These bloody massacres committed by Russians, by Russian soldiers, deserve to be called what they are. This is genocide and it must be judged," Morawiecki told reporters. "This is why we are proposing an international commission to investigate this crime of genocide."

Such a commission "is essential if we want to find out the truth on the extent of Russian fascist crimes." Morawiecki also called for new Western sanctions against Russia and compared Russian President Vladimir Putin to dictators from the past.

"Clear and determined sanctions are necessary. These sanctions are not working," Morawiecki said, addressing Macron saying: "How many times have you negotiated with Putin and what have you achieved? We do not discuss, we do not negotiate with criminals. Criminals have to be fought against."

Addressing German Chancellor Olaf Scholz, Morawiecki said: "It is not the voices of German business leaders, of German billionaires who are probably stopping you from taking action, that should be listened to in Berlin today but the voices of innocent women and children."

The European Union said Monday that it is urgently discussing a new round of sanctions. The 27-nation bloc "will advance, as a matter of urgency, work on further sanctions against Russia," foreign policy chief Josep Borrell said in a statement on behalf of the EU.

"We stand in full solidarity with Ukraine and the Ukrainian people in these somber hours for the whole world," he said.

One EU official told Agence France-Presse (AFP) that a new sanctions package on Russia would be discussed this week. EU foreign ministers could then look it over, either on the sidelines of a NATO meeting happening Wednesday and Thursday or at their regular meeting early next week.

Borrell said in his statement that the EU "condemns in the strongest possible terms" the atrocities reported in Ukrainian towns that had been occupied by Russian forces, including the town of Bucha.

"The massacres in the town of Bucha and other Ukrainian towns will be inscribed in the list of atrocities committed on European soil," Borrell said, adding that "the Russian authorities are responsible for these atrocities, committed while they had effective control of the area."

The statement stressed EU assistance to Ukrainian prosecutors "focused on collection and preservation of the evidences of the war crimes" and its support of probes launched by the International Criminal Court (ICC) and the U.N.'s human rights commissioner.

U.N. Secretary-General Antonio Guterres said he was "deeply shocked" by images of dead civilians in the Ukrainian town of Bucha. An independent investigation that "leads to effective accountability" is essential, he said.

Meanwhile, Ukrainian President Volodymyr Zelenskyy appealed in a video shown 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," Zelenskyy said.

Also Sunday, at least seven people were killed and 34 wounded, including three children, by Russian shelling in Kharkiv in the northeast, Ukraine’s second-biggest city, according to the regional prosecutor’s office. In the Black Sea port of Mykolaiv, regional governor Vitaliy Kim said at least one person died in shelling and 14 were wounded.

Eight people were killed and 34 wounded in Russian attacks on two towns in southern Ukraine on Sunday, prosecutors in Kyiv said.

"The Russian armed forces attacked the cities of Ochakiv and Mykolaiv. Shelling damaged residents' homes, vehicles and civilian infrastructure," the Ukrainian prosecutor general said in a statement on Monday. "As a result of enemy shelling, seven residents of Ochakiv were killed and another 20 were injured. In the city of Mykolaiv, one person died and 14 people were wounded, among them a child," it added.

On the road to Odessa, Ukraine's largest port Mykolaiv was heavily shelled by the Russian army when it unsuccessfully tried to seize it early in its invasion. Thirty-six people were killed late last month when a Russian missile hit a regional government building in the city.

Russia rejects 'provocation' claims

Zelenskyy called the killings evidence of genocide, but Russia’s Defense Ministry rejected the accusation. It 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.

"We categorically reject all allegations," Kremlin spokesperson Dmitry Peskov told journalists. Peskov said that Russian "experts at the ministry of defence have identified signs of video fakes and various fakes."

"We would demand that many international leaders do not rush to sweeping accusations and at least listen to our arguments," he said.

Russia's Foreign Ministry said it would reiterate its request for the U.N. Security Council to meet on Monday over what Moscow called the "criminal provocations by Ukrainian soldiers and radicals" in the town of Bucha.

Britain's mission to the United Nations, which holds the presidency of the 15-member council for April, had said the Security Council would hold a scheduled discussion on Ukraine on Tuesday, and not meet on Monday as requested by Russia.

Russia asked for a meeting Monday of the U.N. Security Council to discuss events in the city. The United States and Britain have recently accused Russia of using Security Council meetings to spread disinformation.

"Today Russia will again demand that the U.N. Security Council convene in connection with the criminal provocations of Ukrainian servicemen and radicals in this city," Russian Foreign Ministry spokesperson Maria Zakharova wrote on her Telegram channel.

The Russian Defense Ministry said the images distributed by Ukraine were "another staged performance by the Kyiv regime," and Russia's chief investigator on Monday ordered a probe on the basis that Ukraine had spread "deliberately false information" about Russian armed forces in Bucha.

Since Feb. 24, thousands of people have been killed and more than 4 million Ukrainians have been forced to flee their country. Russian President Vladimir Putin has said the attack is aimed at eliminating a security threat after Ukraine’s government pursued membership in the U.S.-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 Istanbul, but no written confirmation has been provided. Russian demands include Ukraine declaring itself neutral and renouncing membership in 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 up until March 30.

The reports of atrocities are severe enough that European officials "would have to talk about halting gas supplies from Russia," German Defense Minister 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 nations 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 Gitana Nauseda said on Twitter, referring to Russia as "the aggressor."

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

U.S. Secretary of State Antony Blinken called images of what happened near Kyiv "a punch to the gut" on CNN’s "State of the Union." The United States 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.

One resident of Bucha, who refused to give his name out of fear for his safety, said Russian troops went building to building and took people out of the basements where they were hiding. The resident 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 Zelenskyy, claimed some of the women had been raped before being killed and the Russians then burned the bodies.

Ukraine takes control of northern towns

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.

In a video address posted online Sunday, 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.

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 50 kilometers (30 miles) west of Kyiv, residents told the 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.