A recent series of leaks of data from South Korea’s nuclear operator are a “grave situation” that was unacceptable as a matter of national security, president Park Geun-hye says.

Korea Hydro and Nuclear Power Co Ltd (KHNP), which runs South Korea’s 23 nuclear power reactors, said on Monday its computer systems had been hacked, raising alarm in a country that remains at war with North Korea.

The nuclear operator said only non-critical data had been stolen and operations of the nuclear plants were not at risk.

• North Korea’s internet collapses
• North Korea threatens US strikes
• Dr Evil ‘schools’ North Korea over Sony hack attack

South Korea’s law enforcement authorities have opened an investigation.

“Nuclear power plants are first-class security installations that directly impact the safety of the people,” Ms Park said at a cabinet meeting, according to her office.

“A grave situation that is unacceptable has developed when there should have been not a trace of lapse as a matter of national security.”

She ordered inspections of safeguards at national infrastructure facilities, including the nuclear power plants, against what she called “cyber terrorism”.

Earlier, a South Korean official said Seoul had not ruled out the possible involvement of North Korea in the cyber attack on South Korea’s nuclear power plant operator, although Ms Park did not make any mention of it.

The incident at the nuclear operator came after the United States accused North Korea of a devastating cyber attack on Sony Pictures and vowed to respond proportionately.

The cyber attack prompted the film studio to scrap film The Interview which parodies life in the North.