N Korea says leader's powerful uncle executed

North Korea has executed the uncle of its leader Kim Jong-un days after he was dismissed, state news agency KCNA announced, branding the once-powerful Jang Song-thaek a "traitor".

Jang was executed on Thursday shortly after a special military trial, KCNA reported.

He had been accused of a string of criminal acts including corruption, womanising and drug-taking.

"The accused Jang brought together undesirable forces and formed a faction as the boss of a modern day factional group for a long time and thus committed such hideous crime as attempting to overthrow the state," KCNA said.

The official Rodong Sinmun newspaper on Friday carried a photograph of Jang in handcuffs and being held by uniformed guards as he stood trial.

He had previously held influential positions in the ruling party and the military.

Al Jazeera's Harry Fawcett, reporting from Bangkok, said the execution has laid bare a massive power struggle in the secretive country.

"It's an incredibly public condemnation of this once very powerful man," our correspondent said.

The sacking on Monday suggests Pyongyang is undergoing its biggest leadership upheaval since the death in 2011 of former leader Kim Jong-il, the younger Kim's father. 

'Wild ambition'

KCNA said earlier this week that Jang had been removed from all his posts and expelled from the Workers' Party.

"From long ago, Jang had a dirty political ambition. He dared not raise his head when Kim Il-sung and Kim Jong-il were alive," KCNA said, referring to leader Kim's grandfather and father, who were previous rulers of the dynastic state.

"He began revealing his true colours, thinking that it was just the time for him to realise his wild ambition in the period of historic turn when the generation of the revolution was replaced."

Jang was married to Kim's aunt, the daughter of the North's founding leader Kim Il-sung, and was widely considered to be working to ensure his nephew firmly established his grip on power in the past two years.

Jang had been a prominent fixture in many of the reports and photographs of Kim Jong-un's public activities, but his appearances have tapered off sharply this year and he has not appeared in official media since early November.

US State Department spokesman Patrick Ventrell said the US could not independently verify the execution but had "no reason" to doubt the KCNA report.

"If confirmed, this is another example of the extreme brutality of the North Korean regime," Ventrell said. "We are following developments in North Korea closely and consulting with our allies and partners in the region."