A reactor at a nuclear plant run by Kyushu Electric Power Co. was halted Monday after the utility was unable to complete on schedule anti-terrorism measures required by regulators — the first such suspension under stricter rules introduced after the 2011 Fukushima nuclear crisis.

The No. 1 reactor at the Sendai nuclear power plant in Kagoshima Prefecture was shut down in the afternoon ahead of the Tuesday deadline set for implementing the safety measures.

Kyushu Electric will aim to reboot the unit on Dec. 26 after regular safety checks and completion of necessary facilities.