Ukraine narrowly escaped disaster during fighting at the weekend that rocked Europe’s largest atomic power plant with a barrage of shells, some falling near reactors and damaging a radioactive waste storage building, the U.N. nuclear watchdog said.

It was not clear which side was responsible for the explosions at the Zaporizhzhia nuclear power station, which has been under Russian control since soon after it invaded Ukraine on Feb. 24. Whoever fired on the plant was taking “huge risks and gambling with many people’s live,” said Rafael Grossi, director general of the International Atomic Energy Agency (IAEA). “We were fortunate a potentially serious nuclear incident did not happen.