North Korean computer hackers have stolen hundreds of classified military documents from South Korea including detailed wartime operational plans involving its US ally, a report said Tuesday.

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, Rhee said, according to Daily Mail.

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

Advertisement

The report comes amid heightened fears of conflict on the Korean peninsula, as the North's weapons program soared in recent months with Pyongyang launching a flurry of missiles and conducting its sixth and most powerful nuclear test in defiance of multiple sets of UN sanctions.

Tension is fueled by US President Donald Trump's continued threats of military action against Pyongyang to tame its weapons ambitions.

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

South Korean President Moon Jae-in. Photo / AP
South Korean President Moon Jae-in. Photo / AP

On Monday he again tweeted about the country, saying that the United States "has been unsuccessfully dealing with North Korea for 25 years, giving billions of dollars & getting nothing", adding that "policy didn't work".

Citing Seoul's defence ministry, Rhee said that 80 percent 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.

A ministry spokesman declined to confirm the report, citing intelligence matters.

In May the ministry said North Korea had hacked into Seoul's military intranet but did not say what had been leaked.

Advertisement

Pyongyang has a 6,800-strong unit of trained cyber-warfare specialists, according to the South Korean government.

It has been accused of launching high-profile cyber-attacks including the 2014 hacking of Sony Pictures.

The Chosun Ilbo story was the second report Tuesday of military-related cyber-attacks in the Asia-Pacific.

Australia's government said separately an unidentified defence contractor had been hacked and a "significant amount of data" stolen.

There were 47,000 cyber-incidents in the last 12 months, a 15 per cent increase from the previous year, Minister for Cyber Security Dan Tehan said in Canberra as he launched a report by the Cyber Security Centre.

Tension on the Korean peninsula is fueled by US President Donald Trump's continued threats of military action against Pyongyang to tame its weapons ambitions. Photo / AP
Tension on the Korean peninsula is fueled by US President Donald Trump's continued threats of military action against Pyongyang to tame its weapons ambitions. Photo / AP

The defense contractor was exploited via an internet-facing server, with the cyber-criminals using remote administrative access to remain in its network, the report said.

The Australian newspaper reported that the hacker was based in China but Tehan told the Australian Broadcasting Corporation that "we don't know and we cannot confirm exactly who the actor was".

A spokesman for South Korea's Joint Chiefs of Staff said its military was closely monitoring the movements of the North Korean army and maintaining full readiness in case of further conflict.

Consistent movements of personnel and equipment were being detected in certain locations in the North, Yonhap news agency reported, suggesting that preparations for another weapons test might be under way.

North Korea often uses provocative tests to mark key historical commemorations and the country is celebrating the 72nd anniversary of the founding of the ruling Workers' Party on Tuesday.