Seoul, Dec 22 (IANS): South Korean officials have launched probes into threats of a hacking attack on the country's nuclear reactors, officials said Monday.

The probes were launched after a hacker, who identified himself as the president of anti-nuclear group in Hawaii, demanded shutting down of the three reactors in southeastern South Korea, Xinhua reported.

The hacker Sunday revealed some internal documents, taken from the state-run nuclear plants operator, Korea Hydro & Nuclear Power Co. (KHNP), on a Twitter account. The microblogging account has been named "president of anti-nuclear power group in Hawaii".

South Korean officials have reportedly sought the US investigative authority's assistance as the Twitter account is registered in America.

The plans revealed on the internet included information about floor plans of some reactors' air cooling system, MCNP version 5 manual; an open programme to build reactor core, and BURN4; a calculator programme for nuclear reactors.

It marked the fourth such postings since December 15 when the hacker leaked personal information of around 10,000 employees of the KHNP.

On Friday, the hacker called for shutting down the Gori-1, Gori-3 and Wolsong-2 nuclear reactors in southeast South Korea for three months from Christmas.

The hacker threatened to leak about 100,000 pages of internal documents unless the three reactors were shut down.

The Nuclear Safety and Security Commission and the ministry of trade, industry and energy said in a joint statement that cyber attacks on nuclear reactors would be impossible as reactor-control networks are being run in a completely separate network from outside.

Meanwhile, the KHNP, which operates 23 nuclear reactors that generate about 30 percent of the country's electricity demand, said the leaked documents are not confidential nor related to core technologies.