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 a purported attempt to overthrow its leadership, analysts said, and the first 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 Jang, 67, was executed 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 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 Jang's neck so he would bow before the tribunal. The report from the state news agency did not say how Jang was executed. The North usually executes criminals by a firing squad.
Even before the reported execution, Jang's recent downfall had raised worries in the United States and South Korea that 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 the U.S. military presence in the region.
Jang, believed to have been the second-most powerful man in the country, was the most prominent North Korean purged and executed under Kim, who South Korean officials said was resorting to "a reign of terror" in an attempt to consolidate his power. Jang was the husband of Kim Kyong Hui, a sister of Kim Jong Il, the late North Korean leader and Kim Jong Un's father.
The wife's fate was unknown, although analysts say it would be unlikely for Kim Jong Un to harm a blood relative.
Other family members have been stripped of their posts in the past, but their fates were not clear.
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 Sunday, North Korea stripped Jang of 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 as party members looked on.
At the time, some analysts said the treatment was a sign that Jang would be killed, while others still doubted the young Kim would go that far.
The State Department said Thursday night that it could not independently verify the execution, but a deputy spokeswoman, Marie Harf, said "we have no reason to doubt the official KCNA report."
"If confirmed," she said, "this is another example of the extreme brutality of the North Korean regime. We are following developments in North Korea closely and consulting with our allies and partners in the region."
Given the opaque nature of the North Korean state, it is always possible that the charges against Jang were trumped up and used as a way to remove a powerful man Kim may have worried was a threat.
The KCNA report suggested that Jang started nurturing his own political ambitions even as 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 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 Kim took over the country's leadership after his father's death in December 2011, making him the third generation to run the state.
The report Friday said Jang "committed an unforgivable crime by interfering in the succession of leadership in various means," it said. "He thought his time had come as the revolution of the nation was undergoing a generational change and began showing his true colors."