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

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

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

Pyongyang has denied responsibility in its state media for the cyber attacks, criticising Seoul for “fabricating” claims about online attacks.

Separately on Wednesday, cyber security firm FireEye said in a statement North Korea-affiliated agents were detected attempting to phish U.S. electric companies via emails sent in mid-September, although these attempts did not lead to a disruption in the power supply.

It did not specify when the attempts had been detected or clarify which companies had been affected.