Since Russian troops withdrew from towns and villages around the Ukrainian capital Kyiv, Ukrainian troops have been showing journalists corpses of what they say are civilians killed by Russian forces, destroyed houses and burnt-out cars.

The West says the dead civilians are evidence of war crimes. Reuters saw dead bodies in the town of Bucha but could not independently verify who was responsible for the killings.

"It is a simply a well-directed - but tragic - show," Kremlin spokesman Dmitry Peskov told reporters. "It is a forgery aimed at denigrating the Russian army - and it will not work."

"We once again urge the international community: detach yourself from such emotional perceptions and think with your head," Peskov said. "Compare the facts and understand what a monstrous forgery we are dealing with."

Ukraine says Russia is guilty of genocide and US President Joe Biden on Monday accused Russian President Vladimir Putin of war crimes and called for a trial.

The Kremlin said Biden's remarks were unacceptable and unworthy of a leader of the United States.

The outcry over the discovery of so many dead civilians, some shot in the head, after Russia's withdrawal from areas around Kyiv, has prompted Western promises to impose even tougher sanctions on Russia.

The European Commission is to propose sweeping new sanctions against Russia, including a ban on imports of coal, rubber, chemicals and other products, an EU source told Reuters.

Russia's economy is already heading for its biggest economic contraction since the years following the 1991 fall of the Soviet Union after the West largely cut Russia out of the Western financial system and sanctioned its richest businessmen.

Russia casts the evidence of civilian executions in Bucha as a cyclical ploy by Ukraine and its Western backers, who Moscow says are gripped by discriminatory anti-Russian paranoia.

"These are fakes that matured in the cynical imagination of Ukrainian propaganda," Dmitry Medvedev, who served as president from 2008 to 2012 and is now deputy secretary of Russia's Security Council, said of Bucha.

Medvedev said the fakes had been concocted for vast amounts of money by Western public relations companies and "tame" non-governmental organisations. He did not provide specific evidence.

He suggested that Ukrainian forces had been prepared to kill their own citizens in a bid to discredit Russia.

Russia's defence ministry said it had evidence that the 72nd Ukrainian Main Centre for Psychological Operations had helped stage such propaganda in a village 23km northwest of Kyiv as well as in Sumy, Konotop, and other towns.

Moscow has questioned why, if its forces withdrew from Bucha on March 30 and the mayor of Bucha declared the area free of Russian forces on March 31, that the bodies of dead civilians were only shown for the first time on April 3.

Russia also says the bodies shown in some footage did not show characteristic signs of degradation that would be expected after a number of days.

Australian Associated Press