Ukraine’s President Volodymr Zelenskyy said it is possible that there will be no meeting between him and Russian counterpart Vladimir Putin.

Zelenskyy said olding negotiations with Russia was the only option for his country, but he said it was possible that he and Putin would not personally hold talks, in comments broadcast on national television on Tuesday.

Zelenskyy also said Kyiv will search for possible war criminals and prosecutors of other countries will deal with them.

The Ukrainian president will address the U.N. Security Council on Tuesday, where he is expected to demand tough new sanctions on Moscow over killings in the town of Bucha that he has called "war crimes" and "genocide".

The speech, Zelenskyy's first to the body since Russia's invasion, comes after he made an emotional trip to Bucha, where dozens of bodies were discovered after the withdrawal of Russian troops.

Horrific images of corpses lying in the streets, some with their hands bound behind them, have drawn international condemnation of Russia.

Moscow has denied responsibility and suggested the images are fake or that the deaths occurred after Russian forces pulled out of the area.

But newly released satellite photographs taken by Maxar Technologies in mid-March, before the Russian withdrawal, showed what appeared to be bodies in some of the same places they were later found by Ukrainian troops and seen by journalists.

On Monday, wearing body armour and visibly distressed, Zelenskyy spent half an hour in Bucha, where he blamed Russian troops for the killings.

"These are war crimes and it will be recognised by the world as genocide," he said.

Later in his nightly address, he said "the sanctions response to Russia's massacre of civilians must finally be powerful."

"But... did hundreds of our people have to die in agony for some European leaders to finally understand that the Russian state deserves the most severe pressure?" he asked in the video posted to Telegram.

He also called for additional weapons from Western allies, saying more equipment could have saved thousands.

"I do not blame you -- I blame only the Russian military," he said. "But you could have helped."