Image caption Kim Jong-il is thought to have had a stroke in 2008

North Korea's ruling communist party is to hold a rare meeting of its political bureau, state media have said.

The session will be held in September to select new leaders for the Workers' Party of Korea (WPK), the North Korean Central News Agency said.

Analysts say the move may signal a transition of power in the secretive country.

Leader Kim Jong-il is believed to be in ill health and grooming one of his sons, Kim Jong-un, to succeed him.

The meeting is "for electing [the party's] highest leading body reflecting the new requirements of the WPK", the announcement said.

"We are now faced with the sacred revolutionary tasks to develop the WPK... into an eternal glorious party of Kim Il-sung and further increase its militant function and role to glorify the country as a great prosperous and powerful socialist nation."

Growing role

Kim Jong-il took over as leader from his father, North Korea's founder Kim Il-sung, after his death in 1994.

With Kim Jong-il thought to be in ill health following a suspected stroke in 2008, analysts believe the conference will be held to elevate the status of his third son, Swiss-educated Kim Jong-un.

Earlier this week the director of South Korea's National Intelligence Service said that the 27-year-old is already taking a role in policy-making and frequently accompanies his father on inspection tours.

The BBC's John Sudworth in Seoul says Kim Jong-il himself began his official role to succeed his father by assuming a senior party position at a convention in 1980.

Anniversary tension

The announcement comes a day after the 60th anniversary of the beginning of the three-year war between North and South Korea.

It also follows a warning from the United States to North Korea to refrain from "actions that increase tensions in the region," amid concerns that Pyongyang may be preparing a new round of missile tests.

The US state department said it was aware North Korea had issued a nine-day ban on shipping off its western coast.

Tensions between North and South Korea have increased following the 26 March sinking of a South Korean warship, which an international investigation concluded was sunk by a torpedo from a North Korean submarine.