Ukrainian President Volodymyr Zelenskyy said on the Thursday that the situation in the town of Borodyanka was "significantly more dreadful" than in nearby Bucha, where Russian forces' suspected killings of civilians have been broadly condemned.

Local officials have said more than 300 people were killed by Russian forces in Bucha, 35 kilometers northwest of the capital Kyiv, and around 50 of them were executed. Many corpses were left in the streets, and there had been reports of Russians bringing in mobile crematoria to process -- some say conceal -- some of the dead.

Moscow has denied targeting civilians and says images of bodies in Bucha were staged by the Ukrainian government to justify more sanctions against Moscow and derail peace negotiations.

"The work to clear the rubble in Borodyanka has begun ... It's significantly more dreadful there. Even more victims from the Russian occupiers," Zelenskyy said in a video posted on the Telegram messaging service.

The town is about 25 km from Bucha.

He did not provide any further detail or evidence that Russia was responsible for civilian deaths in the town.

The killing of civilians in the town of Bucha have been widely condemned by the West as war crimes, building pressure for stricter sanctions against Russia.

"And what will happen when the world learns the whole truth about what the Russian military did in Mariupol?" Zelenskyy asked.

"There, on almost every street, is what the world saw in Bucha and other towns in the Kyiv region after the withdrawal of Russian troops."

Moscow says one of the aims of its military campaign is to "liberate" largely Russian-speaking places such as the southern port of Mariupol from the threat of genocide by Ukrainian nationalists, who it says have used civilians as human shields.

Zelenskyy has rejected those claims, saying they are a baseless pretext for Russia's invasion.