North Korean state media has said that Kim Jong-un's uncle has been executed, calling the leader's former mentor "worse than a dog".

The announcement early on Friday comes days after Pyongyang said that Jang Song-thaek had been removed from all his posts because of allegations of corruption, drug use, gambling, womanising and generally leading a "dissolute and depraved life".

Jang was considered the second most powerful official in the country. He was seen as helping Kim Jong-un consolidate power after the death of his father, Kim Jong-il, two years ago. Jang was the latest and most significant in a series of personnel reshuffles that Kim has conducted in an apparent effort to bolster his power.

The state news agency KCNA said a tribunal examined Jang's crimes, including "attempting to overthrow the state by all sorts of intrigues and despicable methods with a wild ambition to grab the supreme power of our party and state".

The report called him "a traitor to the nation" and "worse than a dog".

Some analysts see the purge as a sign of Kim's growing confidence, but there has also been fear in South Korea that the removal of such an important part of the North's government, who was seen by outsiders as the leading supporter of Chinese-style economic reforms, could create dangerous instability or lead to a miscalculation or attack on the South.