"By the grace of God, the world narrowly averted a nuclear catastrophe last night," Linda Thomas-Greenfield told the Security Council.

"Russia's attack last night put Europe's largest nuclear power plant at grave risk," Thomas-Greenfield said.

"It was incredibly reckless and dangerous. And it threatened the safety of civilians across Russia, Ukraine and Europe," she said.

Rosemary DiCarlo, UN undersecretary general for political affairs, told the council that attacks on nuclear power facilities "are contrary to international humanitarian law."

Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), speaking from an airplane on a flight to Iran, said he was prepared to travel to Ukraine to ensure the security of the country's nuclear facilities.