North Korea Says Leader’s Uncle Was Executed as a Traitor

SEOUL, South Korea — North Korea said Friday that Jang Song-thaek, the uncle and presumed mentor of its leader, Kim Jong-un, was executed for plotting a military coup.

The announcement was a highly unusual admission of instability from the reclusive, nuclear-armed country, which normally cloaks any signs of disloyalty to the Kim dynasty that has ruled since the country’s founding. It was the first time in recent decades that the North revealed what it purported was an attempt to overthrow its leadership, analysts said, and the first publicly announced execution of a member of the ruling family.

Calling him a “traitor” and “worse than a dog,” the state-run Korean Central News Agency said Mr. Jang, 67, was executed on Thursday, immediately after he was convicted of treason in a special military court.

“He lost his mind due to his greed for power,” the agency reported. “He persistently plotted to spread his evil design into the military, believing that he could overthrow the leadership if he could mobilize the military.”

North Korea also released a photo of Mr. Jang standing at the military court, with his hands bound. Two State Security agents in military uniforms held his arms while one of them pressed the back of Mr. Jang’s neck so he would bow it before the tribunal. The news agency report did not say how Mr. Jang was executed. The North usually executes criminals by a firing squad.

Even before the reported execution, Mr. Jang’s recent downfall had raised worries in the United States and South Korea that Mr. Kim might lash out, possibly staging another nuclear test or instigating a military provocation against the South. China, the North’s longtime patron, was also unnerved by mounting evidence of an internal power struggle that could destabilize its already troublesome ally and possibly increase an American military presence in the region.

Mr. Jang, believed to have been the second-most-powerful man in the country, was the most prominent North Korean purged and executed under Mr. Kim, who South Korean officials said was resorting to “a reign of terror” in an attempt to consolidate his power. Mr. Jang was the husband of Kim Kyong-hee, a sister of Kim Jong-il, Mr. Kim’s father and the North’s longtime leader.

The fate of Ms. Kim was not known, though analysts say it would be unlikely for Kim Jong-un to harm a blood relative.

Mr. Jang had been a fixture in the North Korean elite for the past 40 years, serving in major party posts under Kim Jong-il. During a party meeting on Sunday, North Korea stripped Mr. Jang of all his powerful posts and expelled him from the ruling Workers’ Party. On Monday, the state-run TV showed the spectacle of the once-powerful man being hauled off from the party meeting by uniformed guards.

At the time some analysts said the treatment was a sign that Mr. Jang would be killed, while others still doubted that Mr. Kim would go that far.

The State Department said Thursday that it could not verify the execution, but a deputy spokeswoman, Marie Harf, said, “We have no reason to doubt the official K.C.N.A. report.”

“If confirmed,” she said, “this is another example of the extreme brutality of the North Korean regime.”

Given the opaque nature of the North Korean state, it is possible that the charges against Mr. Jang were trumped up to remove a powerful man Mr. Kim may have worried was a threat.

The K.C.N.A. report suggested that Mr. Jang started nurturing his own political ambitions even as Mr. Kim’s father began grooming his son to succeed him. If true, his moves would most likely have been seen as a betrayal; at the time many analysts believed Mr. Jang and his wife had been handpicked by Kim Jong-il to help his young and inexperienced son navigate the North’s treacherous politics and carry on the family dynasty. The younger Mr. Kim took over the leadership of the country after his father’s death in late 2011, making him the third generation to run the state.

Chang Yong-seok, a senior researcher at the Institute for Peace and Unification Studies at Seoul National University, said that Mr