Image caption The departure of Ri Yong-ho (L) is being scrutinised for clues about Kim Jong-un's leadership style

North Korean military chief Ri Yong-ho has been removed from all official posts, according to state media.

As well as being head of the army, he was vice-chairman of the powerful Central Military Commission and held top posts in the ruling Workers' Party.

In a short statement, the party said Mr Ri had been removed from his posts "because of illness".

The BBC's Seoul correspondent Lucy Williamson says there is widespread scepticism about that explanation.

The decision to relieve Mr Ri of his duties came at a meeting of the Workers' Party Central Committee politburo on Sunday, state-run news agency KCNA said.

The brief report made no mention of a successor.

In Seoul, a spokesman for the Unification Ministry told reporters that the move was "very unusual".

"It's quite a rare case that the North promptly and publicly announced early this morning the outcome of a meeting yesterday, on 15 July. We will keep monitoring closely," Kim Hyung-suk said.

Key figure

Analysis Ri Yong-ho's removal from office has taken many people outside North Korea by surprise. He was seen as having a key role in the recent transition of power in North Korea, from Kim Jong-il to his son, Kim Jong-un. Few people here are taking the regime's explanation of "illness" at face value. The statement posted on North Korea's state news agency was short and sparse, giving no details of his condition or any indication of his successor as head of the army. Instead, some analysts are reading his removal as a possible political purge - in order to cement Kim Jong-un's grip on the military, or perhaps signalling a rift in the team of senior figures which has encircled the young heir during his six months in power. Analysis: A diplomatic illness?

Mr Ri was made army chief three years ago under Kim Jong-il, the current leader's father who died in December 2011 after ruling North Korea for almost two decades.

The army chief regularly appeared at state occasions beside Kim Jong-il.

He was also one of seven top officials to accompany the younger Kim as he followed the hearse containing his father's body at his state funeral.

Mr Ri was widely thought to be a figure in the inner circle of the new leader and instrumental in helping him cement his position.

His removal is now being scrutinised by analysts for signs of the direction in which Kim Jong-un, seen as young and inexperienced, will take the country.

The army and Workers' Party are the two primary institutions that bolstered the Kim family dynasty, Robert Kelly, a professor at the Pusan National University in South Korea told the BBC.

Ri Yong-ho Ri, 69, appointed army head in 2009

Vice-chairman of the Central Military Commission

Top military official after Kim Jong-un

Key posts in Worker's Party made him a top political figure Powers behind new leader

Kim Jong-un did not serve in either of those two institutions which are ''traditional proving grounds and grooming grounds... for the leadership in the system''.

''So his position is very vulnerable because he does not know the generals and colonels who prop up the state,'' said Dr Kelly.

In April North Korea defied international warnings to launch a rocket - an action its neighbours called a long-range missile test that contravened UN resolutions.

The rocket launch failed, and analysts warned that it was not clear whether this would lead to more efforts to demonstrate military might - such as another nuclear test - or strengthen the position of reformers seeking to focus on the economy.

South Korea warned earlier this year that Pyongyang appeared to be in the late stages of preparing for a third nuclear test - a claim North Korea has denied.

International talks aimed at ending North Korea's nuclear ambitions have been stalled since 2009.