Seoul, Dec 23 (IANS): South Korean President Park Geun-hye Tuesday said leakage of data about nuclear reactors is a serious problem and it should not have happened.

"Nuclear reactors are the most important security facility directly linked to people's safety," Park said during a cabinet meeting.

"Serious situations that should never have happened were caused in terms of national security," Xinhua quoted the president as saying.

Her comments came after a hacker posted blueprints and installation diagrams on the internet taken from the Korea Hydro and Nuclear Power (KHNP) company, the country's nuclear plant operator.

The perpetrator, who identified himself as the "president of anti-nuclear group in Hawaii", claimed that he hacked and infiltrated computer systems of KHNP, threatening the second hacking attack and another leakage of some 100,000 pages of undisclosed documents unless three nuclear reactors in the country are closed by Dec 25.

Park said people are deeply worried as KHNP's blueprints and internal documents were disclosed and the hacker demanded the halting of operations in the nuclear reactors.

She called for prosecutors to make a thorough investigation into the matter.

KHNP operates all 23 nuclear reactors of South Korea.

Its parent company is Korea Electric Power Corp, the state-run power supplier.