A South Korean lawmaker says North Korean hackers may have stolen highly classified military documents that include US-South Korean wartime "decapitation strike" plans against the North Korean leadership, according to South Korean media reports.
The United States, meanwhile, staged another show of force meant to deter any North Korean aggression by flying two B-1B supersonic bombers on Tuesday night from an air base in the US territory of Guam to the South for drills with South Korean jets.
Such flights by the powerful aircraft based in Guam incense the North, which claims they are preparation for war; Pyongyang has threatened to send missiles into the waters around Guam.
If confirmed, the reported hacking attack by the North would be a major blow for South Korea at a time when its relations with rival North Korea are at a low point.
The South has taken an increasingly aggressive stance toward the North's belligerence amid back-and-forth threats of war between North Korea and US President Donald Trump.
North Korea's possession of secret war plans would require a major overhaul of how South Korea and its ally Washington would respond if there's another war on the Korean Peninsula.
An unusually aggressive approach to the North by Trump, which has included rhetoric hinting at US strikes and threatening the destruction of North Korea's leadership, has some South Koreans fearful that war is closer than at any time since the Korean War ended in 1953 in a shaky ceasefire, leaving the Korean Peninsula still technically in a state of war.
Rep Lee Cheol-hee, a lawmaker for the ruling Democratic Party who sits on the National Defence Committee, cited unidentified defence officials as saying the hackers stole the US-South Korean war plans last year, according to news reports on Tuesday.
Lee did not respond to attempts to confirm the stories. Defence officials refused to comment on Wednesday.
Among the classified plans allegedly stolen from the South were said to be blueprints for targeted attacks by Seoul and Washington to eliminate North Korean leader Kim Jong Un if a crisis breaks out or appears imminent.
The South's Yonhap news agency quoted Lee as saying that 235 gigabytes of military documents were taken.
While nearly 80% of the documents had not yet been identified, they reportedly included contingency plans for South Korean special forces and information on military facilities and power plants, it said.
Seoul says North Korea has repeatedly staged cyberattacks on South Korean business and government websites. North Korea routinely denies responsibility.
Not long after the news of the alleged cyberattacks broke, two B-1B bombers few from Guam to conduct drills with two South Korean fighter jets on Tuesday night, a South Korean Defence Ministry official said, requesting anonymity because of department rules.
North Korea has yet to comment on either the bombing drills or the hacking claims.