The head of the U.N. atomic watchdog said the physical integrity of the Russian-occupied Zaporizhzhia nuclear plant in Ukraine had been violated several times and he was worried by the situation there.
IAEA chief Rafael Grossi was speaking after spending several hours at the plant on Thursday, braving gunfire he said had come "uncomfortably close".
He and his team of U.N. experts were returning on Friday across the frontlines to assess physical damage to Europe's biggest nuclear energy plant.
The site was captured by Russian forces soon after they invaded Ukraine in late February and has become a focus of deep concern over the possibility that shelling in the vicinity could cause a nuclear disaster.
Moscow and Kyiv blame each other for the shelling. Kyiv accuses Moscow of using the facility to shield its forces, a charge Moscow denies while rejecting calls to withdraw its troops. The plant is still run by Ukrainian staff.
Mr. Grossi said on his return to Ukrainian-held territory on Thursday: "It is obvious that the plant and the physical integrity of the plant has been violated, several times ... this is something that cannot continue to happen."
He said his experts would stay at the facility and he would continue to worry until the situation had stabilised.
Mr. Grossi said he had been able to tour the entire site, seeing key areas such as the emergency systems and control rooms. His team would now need to do a lot of work to finish its analysis of technical aspects.
"We are not going anywhere. The IAEA is now there, it is at the plant and it is not moving - it's going to stay there," Mr. Grossi told reporters once he had crossed back into Ukrainian-held territory.
Those experts, he said, would provide what he called an impartial, neutral, technically sound assessment of what was happening on the ground.
The IAEA team was delayed several hours by shelling near the site of the plant.
"There were moments where fire was obvious, heavy machine gun, artillery mortars, at two or three times (it was) really very concerning I would say for all of us," Mr. Grossi said.
One of the plant's reactors was forced to shut down on Thursday due to shelling.
Ukrainian President Volodymyr Zelensky reiterated his calls that all troops be removed from the plant—a demand supported by Kyiv's Western allies and the United Nations.
"The main thing that must happen is the demilitarisation of the station's territory," Mr. Zelensky said in a video address.
Russian Foreign Minister Sergei Lavrov said on Thursday Moscow was doing everything to ensure that the plant could operate safely, and for the IAEA inspectors to be able to complete their tasks.
Several towns near the plant came under Russian shelling on Thursday, Zaporizhzhia regional council mayor Mykola Lukashuk said. Reuters was unable to independently confirm this.
The plant sits on the south bank of a huge reservoir on the Dnipro River that divides Russian and Ukrainian forces in central southern Ukraine. Before the war, it supplied more than a fifth of Ukraine's electricity.
Ukraine started an offensive this week to recapture territory in southern Ukraine, mainly further down the Dnipro in neighbouring Kherson province.
Both sides have claimed battlefield successes in the new Ukrainian push, although details have been scarce so far, with Ukrainian officials releasing little information.
Ukraine's southern command spokesperson, Natalia Humeniuk, said on Friday Ukrainian troops had destroyed ammunition depots and pontoon bridges to hamper movement of Russian reserves.
"Our successes are convincing and soon we will be able to disclose more information," she said.
Moscow has denied reports of Ukrainian progress and said its troops had routed Ukrainian forces.
Reuters could not independently verify those claims.
Ukraine's general staff on Friday said Russian forces had shelled dozens of cities and towns including Kharkiv—Ukraine's second largest city—in the north and Donetsk in the east.
More than seven million people have fled Ukraine, thousands have been killed and cities have been reduced to rubble in what Kyiv and the West call Russia's unprovoked war of aggression.
Moscow calls its actions a "special military operation" to rid Ukraine of nationalists and protect Russian-speaking communities.