China kept silent on Friday about a reported visit by North Korea's secretive leader Kim Jong-il that analysts say is to line up Beijing behind his dynastic succession plans.

Coinciding with Kim's visit to China, former U.S. President Jimmy Carter left Pyongyang on Friday with an American, Aijalon Mahli Gomes, who had been jailed for illegally entering the country.

There was no indication that Carter met Kim, although state media in the North said number two leader Kim Yong Nam had told Carter that Pyongyang was committed to denuclearising the peninsula and resuming six-way talks.

There has been heightened tensions on the Korean peninsula after the March torpedoing of a South Korean navy ship, blamed by Seoul on the North. Pyongyang denies sinking the ship.

South Korea and the U.S. have said resuming the talks will be impossible until the ship sinking dispute is settled.

South Korean officials have said Kim appeared to have been in northeast China since Thursday, possibly accompanied by his youngest son who may be his heir apparent.

There have been no firm sightings of the 68-year-old, who has appeared frail and gaunt since suffering a stroke in 2008, but a riverside hotel in the northeast city of Jilin was under heavy police guard on Friday morning, a practice seen with previous visits and a clue he may have spent the night there.

A motorcade with more than 30 black cars and a military truck later swept out of the hotel, heading in the direction of the nearby city of Changchun along a guarded expressway.

Kim may be seeking approval for succession plans from China, his beleaguered country's key economic and political backer, but Beijing is unlikely to shed any details as the two countries are deeply secretive about their dealings.

CHINA TOP PRIORITY

By passing up the publicity of a meeting with Carter and instead apparently visiting China, Kim showed how much store he placed in ties with Beijing, said John Park, an expert on North Korea at the United States Institute of Peace in Washington D.C.

It would be propaganda coup for Kim Jong-il to meet with Jimmy Carter, and for him to pass that up, one wonders what the Chinese are offering, said Park.

The Workers' Party (WPK), which rubber stamps major policy decisions in the secretive North, is due to hold a rare meeting in September at which the assembly could set in motion the succession of the leader's son, Kim Jong-un, analysts say.

Many analysts say Kim appears in failing health, and some say he may be in a hurry to secure his son's succession to the dynasty that has ruled North Korea since its founding after World War Two.

...with the big party meeting in September, you have what many people believe is Kim Jong-il's last shot at passing the baton, said Park.

China has only officially confirmed Kim's previous visits after he left, and there have no reports this time in the either country's state-controlled media.

It would be the second time since May that Kim has visited, China, which helps prop up North Korea's frail economy.

(Additional reporting by Jack Kim and Jeremy Laurence in Seoul, Tabassum Zakaria in Washington and Chris Buckley in Beijing; Writing by Chris Buckley; Editing by David Fox)

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