Hackers from North Korea are reported to have stolen a large cache of military documents from South Korea, including a plan to assassinate North Korea's leader Kim Jong-un and wartime operational plans involving its US ally.

Rhee Cheol-Hee, a lawmaker for the ruling Democratic party, said the hackers had broken into the South's military network last September and gained access to 235 gigabytes of sensitive data, the Chosun Ilbo daily reported.

Among the leaked documents was Operational Plans 5015 for use in case of war with the North and including procedures for "decapitation" attacks on leader Kim Jong-un, the paper quoted Rhee as saying.

Rhee, a member of parliament's defence committee, could not be reached for comment but his office said he had been quoted correctly.

The report comes amid heightened fears of conflict on the Korean peninsula, fuelled by US President Donald Trump's continued threats of military action against Pyongyang.

In his latest tweet over the weekend, Trump reiterated that diplomatic efforts with North Korea have consistently failed, adding that "only one thing will work".

Citing Seoul's defence ministry, Rhee said that 80 per cent of the leaked documents had yet to be identified.

But the contingency plan for the South's special forces was stolen, he said, as well as details about annual joint military drills with the US and information on key military facilities and power plants

Source: Khaleej Times