SEOUL, South Korea -- A South Korean lawmaker said Tuesday that North Korean hackers may have stolen highly classified military documents that include U.S.-South Korean wartime "decapitation strike" plans against the North, according to South Korean media reports.

Rep. Lee Cheol-hee, a lawmaker for the ruling Democratic Party, cited unidentified defense officials as saying the hackers stole the plans last year, according to the reports. Neither Lee nor Defense Ministry officials responded to attempts late Tuesday to confirm the stories. Defense officials refused to comment when reached by other media.

If confirmed, such a hack would be a major blow for South Korea at a time when its relations with 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 President Trump.

At a press gaggle on Tuesday, Pentagon spokesperson Col. Rob Manning would not confirm the cyberattack. He would only say the U.S. and South Korea work together to defend against cyberthreats.

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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. Kim is the third generation of his family to rule North Korea.

The South's Yonhap news agency quoted Lee as saying that 235 gigabytes of military documents were taken. While nearly 80 percent 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.

Yonhap said South Korean defense officials said in May that North Korea may have hacked a crucial South Korean military online network but didn't say what was stolen.

Seoul says North Korea has repeatedly staged cyberattacks on South Korean business and government websites. North Korea routinely denies responsibility.