SEOUL, South Korea — North Korea has executed its special envoy to the United States on spying charges, as its leader, Kim Jong-un, has engineered a sweeping purge of the country’s top nuclear negotiators after the breakdown of his second summit meeting with President Trump, a major South Korean daily reported on Friday.

Kim Hyok-chol, the envoy, was executed by firing squad in March at the Mirim airfield in a suburb of Pyongyang, the North Korean capital, Chosun Ilbo, South Korea’s largest daily, reported on Friday, citing an anonymous source. Mr. Kim faced the charge that he was “won over by the American imperialists to betray the supreme leader,” the newspaper said.

Four officials of the North Korean Foreign Ministry were also executed, the South Korean daily reported, without providing any hint of who its source might be or how it obtained the information.

South Korean officials could not confirm the Chosun Ilbo report. North Korea has not reported any execution or purge of top officials in recent months. The country remains the world’s most isolated, and outside intelligence agencies have sometimes failed to figure out or have misinterpreted what was going on in the closely guarded inner circles of the country’s leader, Kim Jong-un.