North Korea confirmed Monday that the powerful uncle of the nation's young leader Kim Jong-Un has been purged, accusing him of being a corrupt, drug-using womaniser in a move analysts said cements Kim's grip on power.

Jang Song-Thaek, once seen as his nephew's mentor and the power behind the throne, has been stripped of all his posts for committing criminal acts and leading a "counter-revolutionary faction", state media said.

Analysts said that Jang's main role had been to ensure a smooth transition after the inexperienced Kim Jong-Un succeeded his father in 2011, and that he had become increasingly resented by the leader, who is around 30 years old.

"Jong-Un has built a solid power base for the past two years, and he no longer needed a regent who appeared to be increasingly powerful and threatening," said Paik Hak-Soon, a researcher at the South's Sejong Institute think tank.

Confirmation of his downfall came after South Korea's spy agency said last week that Jang had been purged and two associates executed, in the secretive nation's biggest political upheaval since the death of Kim Jong-Il.

State news agency KCNA said that at a meeting on Sunday, a top body of the ruling Workers' Party confirmed it had "eliminated Jang and purged his group, unable to remain an onlooker to its acts any longer".

The regime said it removed Jang and his associates for seeking to build a faction within the party, appointing his followers to top positions in order to serve his own political ambitions.

The KCNA report said Jang "had improper relations with several women and was wined and dined at back parlours of deluxe restaurants", becoming "affected by the capitalist way of living".

"Ideologically sick and extremely idle and easy-going, he used drugs and squandered foreign currency at casinos while he was receiving medical treatment in a foreign country under the care of the party," it said.

Jang was also accused of hindering North Korea's state-run production of iron, fertilisers and vinalon -- a home-grown synthetic fibre -- by selling off resources at cheap prices and "throwing the state financial management system into confusion".

'Storm of purge' coming

"Prompted by his politically motivated ambition, he tried to increase his force and build his base... Jang and his followers committed criminal acts baffling imagination and they did tremendous harm to our party and revolution," KCNA added.

Kim Jong-Un took over after his father and longtime ruler died in December 2011, in the second succession of a dynasty that has ruled the isolated communist state under a pervasive personality cult.

Jang has fallen out of favour before. In 2004 he was understood to have undergone "re-education" as a steel mill labourer because of suspected corruption, but he made a comeback the following year.

He expanded his influence rapidly after Kim Jong-Il suffered a stroke in 2008 and he was appointed vice chairman of the top military body, the National Defence Commission, in 2010.

His wife and Kim Jong-Il's sister, Kim Kyoung-Hui, has also long been at the centre of power. She was promoted to four-star general at the same time as Kim Jong-Un in 2010.

The pair were once viewed as the ultimate power couple in Pyongyang, but in the past year Kim Kyong-Hui has been less visible, with reports that she was seriously ill and had sought hospital treatment in Singapore.

"This time, Jang is gone for good. He'll never be allowed into politics again," said Paik from the Sejong Institute.

Yang Moo-Jin, a professor at the University of North Korean Studies in Seoul, said it could spark a sweeping purge targeting those loyal to Jang.

"There will be a storm of purge across the country... so Kim Jong-Un becomes the one and only centre of power challenged by no one," he said.

Jang had for decades forged an extensive network of friends in the party and the government, said Kim Kwang-Jin, analyst at the Institute for National Security Strategy and a defector who once worked under Jang handling party finances.

"After two of his associates were executed, now the next target will be those who used to be working at state bodies once supervised by Jang," Kim said, citing the police agency and state bodies related to finance and economy.

"This is a very serious and grave situation," Kim said.

In another indication of an official purge, state TV edited Jang out of a documentary film about Kim Jong-Un.
News reports about Jang, his wife and the two associates recently executed also have been deleted from the KCNA website, with a search for their names producing no results.

Seoul was "closely monitoring" the situation in the North, unification ministry spokesman Kim Eui-Do said.