Ukraine’s Zaporizhzhya Nuclear Power Plant lost its main power connection on Sunday, forcing it to rely on backup electricity for reactor cooling, the U.N.’s nuclear power agency said Sunday.

There was no reported timeline for repairing the line. It is the latest in a string of power disruptions to Europe’s largest nuclear power plant, which sits directly on the frontlines of Russia’s war in Ukraine. 

International Atomic Energy Agency (IAEA) personnel at the plant also heard several rockets fired from a multiple-launch rocket system close to the plant, Director General Rafael Mariano Grossi said in a statement.

“Today’s events once again clearly demonstrate the extremely fragile nuclear safety and security situation at the Zaporizhzhya Nuclear Power Plant,” Grossi said. “I remain deeply concerned about nuclear safety and security at the plant, both when it comes to its vulnerable off-site power supplies – which can be affected by attacks far away from the site – and the more direct military risks it is facing. … In this context, the apparent firing of rockets from near the plant is a special source of concern.”

A short circuit that occurred around 60 miles north of the plant caused the cut in the connection to its sole remaining 750-kilovolt power line – the last of four it had prior to the war – at around 10:30 a.m. local time, the IAEA said.

The plant is still drawing external power from a 330-kilovolt backup power line. An emergency diesel generator also started operating to supply reactor unit 4 after the power loss. The diesel generator was manually shut down after ten minutes, the IAEA said.

Plant personnel are working to repair the larger main power supply line, but it was not clear when it will be reconnected.

The ZNPP has lost external power supply at least seven times since the war began in February 2022. On each of those occasions, emergency diesel generators kicked on to provide the electricity needed for nuclear safety and security functions, including reactor cooling. The connection to the 750-kilovolt line was last lost on August 10, when the line disconnected and was reconnected twice on the same day, the IAEA said.