KYIV/NEW YORK • Russia and Ukraine accused each other of shelling Europe’s biggest nuclear power plant as the U.N. chief proposed a demilitarized zone at the site amid fears of a catastrophe.

Ukraine’s Energoatom agency said the Zaporizhzhia complex was struck five times on Thursday, including near where radioactive materials are stored. Russian-appointed officials said Ukraine shelled the plant twice, disrupting a shift changeover, Russia’s TASS news agency said.

The U.N. Security Council met on Thursday to discuss the situation. Secretary- General Antonio Guterres called on both sides to halt all fighting near the plant.

“The facility must not be used as part of any military operation. Instead, urgent agreement is needed at a technical level on a safe perimeter of demilitarization to ensure the safety of the area,” Guterres said in a statement.

Russia seized Zaporizhzhia in March after invading Ukraine on Feb. 24. The plant, near the front line in the fighting, is held by Russian troops and operated by Ukrainian workers.

At the Security Council meeting, the United States backed the call for a demilitarized zone and urged the International Atomic Energy Agency to visit the site.

Russia’s U.N. Ambassador Vassily Nebenzia said the world was being pushed “to the brink of nuclear catastrophe, comparable in scale with Chornobyl.” He said IAEA officials could visit the site as soon as this month.

Reuters could not independently verify the reports from either side about circumstances at the plant.

Ukrainian President Volodymyr Zelensky demanded Russia return the plant to Ukraine’s control.

“Only a full withdrawal of the Russians ... and the restoration of full Ukrainian control of the situation around the station can guarantee a resumption of nuclear security for all of Europe,” he said in a video address.

France echoed Zelensky’s demand and said Russia’s occupation of the site endangered the world.

“The presence and actions of the Russian armed forces near the plant significantly increase the risk of an accident with potentially devastating consequences,” the French foreign ministry said in a statement.

Kyiv and Moscow have previously blamed each other for attacks on the site. Ukraine has also accused Russia of firing rockets at Ukrainian towns from around the captured nuclear power plant in the knowledge it would be risky for Ukraine to return fire.

Separately, satellite pictures released on Thursday showed devastation at an air base in Russian-annexed Crimea. It suggested Ukraine may have new long-range strike capability with potential to change the course of the war, Western military experts said.

Images from independent satellite firm Planet Labs showed three near-identical craters where buildings at Russia’s Saki air base had been struck with apparent precision. The base, on the southwest coast of Crimea, suffered extensive fire damage with at least eight destroyed warplanes clearly visible.

Russia has denied aircraft were damaged and said explosions at the base on Tuesday were accidental. Ukraine has not publicly claimed responsibility for the attack.

Referring to the damage, Ukrainian presidential adviser Mykhailo Podolyak told Reuters in a message: “Officially, we are not confirming or denying anything ... bearing in mind that there were several epicenters of explosions at exactly the same time.”