A plan to assassinate Kim Jong Un and preparations for a potential nuclear showdown with North Korea were among the trove of South Korean military documents reportedly stolen by Hermit Kingdom hackers.

South Korea’s Defense Ministry did not comment on the alleged hack, which reportedly occurred in September 2016 but was only revealed Tuesday. Rhee Cheol-hee, a lawmaker in South Korea, confirmed the data breach to the BBC. The hack consisted of 235 gigabytes of military documents and about 80 percent of what was stolen hasn’t been identified.

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South Korea announced in May a “large amount of data” was stolen during a cyberattack that was possibly orchestrated by Kim Jong Un’s rogue regime. That same month, Yapizon, a South Korean cryptocurrency exchange, announced 3,816 bitcoins — online currency that amounts to about $5.3 million — was taken on April 22. The company did not disclose who it believed to be the culprit, but security firm FireEye noted North Korean hackers were also suspected of targeting online currency providers.

North Korea denied stealing the documents, the BBC reported. The country celebrated the anniversary of the establishment of the Worker’s Party Tuesday and Pyongyang’s first nuclear bomb test on Monday.

Pentagon spokesman Army Col. Rob Manning told reporters on Tuesday: "I can assure you that we are confident in the security of our operations plans and our ability to deal with any threat from North Korea."

Manning would not confirm the hack.

Pyongyang is suspected of having expert hackers attack South Korean government websites and facilities for years. North Korea has accused its neighbor of “fabricating” the claims, the BBC reported.

News of the hack comes amid increasing tensions in the region.

Defense Secretary Jim Mattis on Monday said the U.S. has “military options that [President Trump] can employ if needed.”

"There's one thing the U.S. Army can do, and that is you have got to be ready to ensure that we have military options that our president can employ if needed," Mattis said during an Army conference in Washington, D.C. "We currently are in a diplomatically led effort.”

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Trump, meanwhile, has continued his attacks against “little rocket man” Kim Jong Un and his regime, with the president taking to Twitter early Monday to say more than two decades of U.S. policy toward North Korea “didn’t work.”

“Our country has been unsuccessfully dealing with North Korea for 25 years, giving billions of dollars & getting nothing. Policy didn’t work!” Trump wrote.

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The weekend tweets came after the president’s Thursday meeting with senior military leaders and their spouses, where he cryptically told reporters “this might be the calm before the storm.” When asked to elaborate on Friday, Trump said, “You’ll find out.”

North Korean state media announced on Sunday Kim Jong Un promoted his sister, Kim Yo Jong, to become an alternate member of the country’s top decision-making body, the politburo. The decision came the same weekend Kim declared his country’s nuclear weapons a “powerful deterrent firmly safeguarding the peace and security in the Korean Peninsula and Northeast Asia” against “protracted nuclear threats of the U.S. imperialists.”

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.