The United States and its allies strongly denounced Russia at the United Nations on Friday for shelling and seizing Europe’s largest nuclear power facility overnight in Ukraine, and some insisted that Moscow not allow such an action to happen again.

Many of the Security Council’s 15 envoys voiced “grave worry” and astonishment, warning against a replay of the 1986 Chernobyl tragedy, the worst nuclear accident in history, which occurred in Ukraine when it was a part of the Soviet Union.

They stated that the strike violated international humanitarian law and asked Moscow to cease from any military activities against nuclear facilities and to enable Ukrainian staff to enter the plant to do their duties.

“The world nearly spared a nuclear disaster last night,” U.S. Ambassador to the United Nations Linda Thomas-Greenfield told an emergency Security Council meeting summoned following Russian soldiers’ takeover of the Zaporizhzhia nuclear power station in southern Ukraine.

“Russia’s attack last night put Europe’s largest nuclear power plant at grave risk. It was incredibly reckless and dangerous. And it threatened the safety of civilians across Russia, Ukraine and Europe,” Thomas-Greenfield said.

As shells hit the area early on Friday, a blaze broke out in a training building – triggering a spasm of alarm around the world before the fire was extinguished and officials said the facility was safe.

Ukraine ambassador to the U.N. Sergiy Kyslytsya called for all Russian forces to be withdrawn from the plant and a no-fly zone over the country to protect the civilian population from air attacks.

Officials remained worried about the precarious circumstances, with Ukrainian staff operating under Russian control in battlefield conditions beyond the reach of administrators.

“France strongly condemns this attack on the integrity of a nuclear structure, which we need to guarantee,” Nicolas de Riviere said in his speech. “The results of the aggression of Russia against Ukraine are possibly devastating for human health and the environment,” he added.

United Kingdom ambassador to the United Nations Barbara Woodward said: “It must not happen again. Even in the midst of an illegal invasion of Ukraine, Russia must keep fighting away from and protect the safety and security of nuclear sites.”

International Atomic Energy Agency chief Raphael Grossi described the situation as “normal operations, but in fact there is nothing normal about this.”

Thousands of people are believed to have been killed or wounded and more than 1 million refugees have fled Ukraine since Russian began its invasion on Feb. 24. Western nations retaliated with sanctions that have plunged Russia into economic isolation.

Russia’s envoy to the United Nations Vassily Nebenzia dismissed Western uproar over the nuclear power plant and called Friday’s Security Council meeting another attempt by Ukrainian authorities to create “artificial hysteria”.

“At present, the Zaporizhzhia nuclear power plant and adjacent territory are being guarded by Russian troops,” he said.

Separately, France and Mexico are working on a resolution to the U.N. Security Council next week that will address the humanitarian impact of Russia’s invasion, diplomats said.