Kyushu Electric Power Co. said Thursday it will halt two reactors next year due to a delay in implementing anti-terrorism measures required by regulators, in the first such suspension under stricter rules set after the 2011 Fukushima nuclear crisis.

The power company said it will shut down the Nos. 1 and 2 reactors at the Sendai nuclear power plant in Kagoshima Prefecture in March and May and plans to restart them in December 2020 and January 2021, respectively, after the installation of necessary facilities.

Under tighter requirements introduced in 2013 by the Nuclear Regulation Authority, nuclear plant operators are required to build facilities that are able to maintain the cooling of nuclear reactors via remote control and prevent the massive release of radioactive materials, even if the units come under attack.

In April the regulator had refused the company's request to postpone the deadlines for the completion of the facilities' construction — March 17 for reactor No. 1 and May 21 for No. 2. The two units will be temporarily closed the day before the deadline.

Kyushu Electric estimates the suspension of the two reactors will raise costs by ¥8 billion ($74.71 million) a month, since the company would need to offset the resulting shortage of power generation with gas-fired power plants.

The No. 1 reactor has been temporarily halted for regular inspection. Kyushu Electric plans to reboot it in early November, before halting it four months later.

All reactors in Japan were suspended after the Fukushima disaster in March 2011. The government introduced the new rules to resume nuclear power generation, as it aims to have nuclear power provide 20 to 22 percent of the country's electricity in 2030.