N Korea alleged to have stolen military data from US, South

North Korean hackers stole a huge trove of classified US and South Korean military documents last year, including a plan to "decapitate" the leadership in Pyongyang in the event of war, a lawmaker in Seoul said on Tuesday.

Rhee Cheol-hee, a lawmaker in the ruling Democratic Party and a member of the parliamentary national defence committee, said North Korean hackers broke into the Defence Integrated Data Center in September last year to steal secret files, including American and South Korean "operational plans" for wartime action. The data centre is the main headquarters of South Korea's defense network.

The Pentagon said on Tuesday that it is aware of reports that North Korea stole wartime operational plans of the United States and South Korea but assured that the information is secure.

The purported revelations come at a time of heightened tensions over North Korea. President Donald Trump recently said that "only one thing will work" when it comes to Pyongyang, hinting that he thinks diplomatic efforts are proving futile and military action may be necessary.

The US military flew two strategic bombers over the Korean peninsula in a show of force late on Tuesday, as President Donald Trump met top defence officials to discuss how to respond to any threat from North Korea.

The two US Air Force B-1B bombers were joined by two F-15K fighters from the South Korean military after leaving their base in Guam, South Korea's Joint Chiefs of Staff said in a statement today.

According to Rhee, the stolen documents included OPLAN 5015, a plan drafted two years ago for dealing with full-blown war with North Korea and said to include procedures to "decapitate" the North Korean leadership. He said the cache also included OPLAN 3100, outlining the military response to infiltration by North Korean commandos or another local provocation, as well as a contingency plan in case of a sudden change in North Korea.

Pentagon spokesman Army Col Robert Manning said Tuesday he was aware of media reports of the breach but would not say if sensitive operation documents were exposed.

"We are confident in the security of our operations plans," Manning said.

While the two Koreas have technically been on a war footing since the Korean War ended in an armistice in 1953, anything that suggests the death or ouster of North Korea's leader, or his assassination, is tantamount to heresy in the North, where the ruling Kims are treated like gods, The Washington Post reports.

Rhee made his claims about the alleged cyberattack to South Korean reporters, citing documents obtained from the defence ministry under a freedom of information request. Rhee's aides told The Washington Post on Tuesday that the lawmaker had collected information from several sources with knowledge of the cyberattacks, and they confirmed that local media had correctly reported Rhee's remarks.

Yonhap News Agency, citing Rhee, reported that the hackers took 235 gigabytes of military documents and that almost 80 per cent of the stolen documents have not yet been identified.

The documents also included reports on key South Korean and US military personnel, the minutes of meetings about South Korean-US military drills, and data on military installations and power plants in South Korea, reported the Chosun Ilbo, South Korea's largest newspaper.

"I can't reveal further details because they are a military secret," Rhee said, according to the paper.

The US and South Korean militaries have a mutual defence pact under which the American military would assume operational control of the alliance if a war breaks out. The two militaries conduct large-scale drills twice a year, rehearsing the responses to various scenarios on the Korean Peninsula.

As Kim has accelerated his nuclear weapons program and aimed increasingly bellicose threats at the allies, those plans have been updated to include "beheading operations" - strikes designed to take out North Korea's leaders.

South Korea's defence ministry declined to confirm or comment on the reports of a cyberattack.

This is far from being the first time that North Korean leader Kim Jong Un's regime has been accused of outrageous cyber attacks. The country's spy agency, the Reconnaissance General Bureau, is thought to have trained and assembled a large cyber army, assumed to be based in China, to launch these kinds of hacks.

North Korea is alleged to have been behind numerous attacks on South Korea's financial networks and government systems and was blamed for the hacking of Sony Pictures Entertainment in 2014, apparently as retaliation for the movie 'The Interview', which culminates with Kim's death in an explosion.

Most recently, North Korea was accused of being behind a cyberattack last year on Bangladesh's central bank that netted $81 million and of masterminding the WannaCry ransomware that rocketed around the world earlier this year.