North Korean hackers may have stolen a large amount of classified military documents, including the latest South Korea-US wartime operational plan, a South Korean ruling party lawmaker said, Yonhap News reported on Tuesday.

Democratic Party representative Rhee Cheol-hee said 235 gigabytes of military documents were taken from the Defense Integrated Data Centre, citing information from unnamed defence officials, Yonhap News reported.

The contents of about 80 per cent of the data have not yet been identified, Yonhap reported, citing Rhee, adding that the hack took place in September last year.

Pyongyang has denied responsibility for the cyberattacks, Yonhap reported, criticizing Seoul for ‘fabricating’ claims about online attacks.

Neither Rhee Cheol-hee, nor his office, was immediately available for a comment.