Seoul: North Korean hackers stole a large amount of classified military documents, including South Korea-US wartime operational plans to wipe out the North Korean leadership, a South Korean ruling party lawmaker said on Wednesday.

Democratic Party representative Rhee Cheol-hee said in radio appearances on Wednesday that 235 gigabytes of military documents were taken from the Defense Integrated Data Center in September last year, citing information from unnamed South Korean defence officials.

This May an investigative team inside the defence ministry announced the hack had been carried out by North Korea, but did not disclosed what kind of information had been taken.

Pyongyang has denied responsibility for the cyberattacks in its state media, criticising Seoul for ‘fabricating’ claims about online attacks.

Rhee, currently a member of the National Assembly’s committee for national defence, said about 80 percent of the hacked data has not yet been identified, but that none of the information was expected to have compromised the South Korean military as it was not top classified intelligence.

Some of the hacked data addressed how to identify movements of members of the North Korean leadership, how to seal off their hiding locations, attack from the air before eliminating them, the lawmaker had said.

These plans had likely not been classified properly but defence ministry officials told Rhee the hacked documents were not of top importance, he said.

Rhee said on Wednesday the hack had been made possible via ‘a simple mistake’ after a connector jack linking the military’s intranet to the internet had not been eliminated after maintenance work had been done on the system.

The South Korean Defence Ministry’s official stance is that they cannot confirm anything the lawmaker said in terms of the hacked content due to the sensitivity of the matter.

In Washington, the Pentagon said it was aware of the media reports but would not comment on the potential breach.

‘Although I will not comment on intelligence matters or specific incidents related to cyber intrusion, I can assure you that we are confident in the security of our operations plans and our ability to deal with any threat from North Korea,’ Pentagon spokesman Colonel Robert Manning told reporters.