The North Korean government laid out its claims of a plot against Mr. Kim in surprising detail on Friday.

It said that officers at South Korea’s National Intelligence Service had trained the man in the assassination plot, and provided him with $20,000 and a satellite communication device. His handlers then sent the “human scum” into North Korea, giving him instructions last year on how to assassinate Mr. Kim, according to a spokesman for the North’s Ministry of State Security. The ministry serves as the North’s intelligence and secret police agency.

The plan involved bombing a military parade attended by Mr. Kim, the North Korean statement said. The South Korean spy agency later provided the man with additional cash to hire co-conspirators, the statement said.

The statement then threatened that an “anti-terrorist attack will be commenced from this moment to sweep away the intelligence and plot-breeding organizations of the U.S. imperialists and the puppet clique, the most mean and brutal hideous terrorist group in the world.” In North Korean propaganda, South Korea is regularly referred to as a puppet of the United States.

In recent years, at least three South Koreans have been arrested in North Korea and sentenced to long prison terms on espionage charges. The North is also holding at least three Americans on charges of “hostile acts,” including a Korean-American named Kim Dong-chul, whom it accused of spying for the South.

It remains impossible to verify these claims. South Korea’s National Intelligence Service dismisses them as propaganda.

North Korea has also made improbable allegations that more than 30,000 North Korean defectors who fled to South Korea in the last two decades were kidnapped by the South.