The head of the U.N.’s global nuclear watchdog agency, the International Atomic Energy Agency, warned Monday that “military operations at nuclear power facilities of Ukraine have caused unprecedented danger of a nuclear accident, risking the lives of people living in Ukraine and in neighboring countries, including Russia.”

Director General Rafael Mariano Grossi told the IAEA’s Board of Governors the agency was still monitoring the huge nuclear plant seized by Russian forces late last week after a rocket or missile struck an administrative building on the compound, “causing a fire but no release of radiation.”

“It was a close call,” said Grossi, adding that “such a situation must not, under any circumstances, be repeated.”

He noted that Russian forces were in control of the Zaporozhye nuclear power plant — the largest in all of Europe — and approving “technical decisions made by the Ukrainian operators” who have been largely deprived of communication with the outside world. 

Grossi said it was “not a safe way to run a nuclear power plant.”

“I am deeply concerned about this turn of events,” he stressed, reiterating the IAEA’s willingness to send a team into Ukraine to help secure that and other facilities. Russia seized the decommissioned Chernobyl plant last month, and its forces have reportedly encircled another facility in the south of Ukraine.

“We’re ready to deploy. We can, and are ready, to assist,” the IAEA chief said, adding that he was personally “willing to travel to Chernobyl, but it can be anywhere, as long as it facilitates this necessary and urgent action.”