Former President Jimmy Carter is returning to the United States from his North Korean "private humanitarian trip" with released American citizen Aijalon Mahli Gomes.

Carter arrived in North Korea Monday for discussions regarding Gomes, 31, from Boston. Gomes was sentenced in April to eight years of hard labor for illegally entering North Korea from China.

Carter was met at the North Korean capital Pyongyang's airport by officials including North Korean deputy leader Kim Yong Nam.

Prior to Carter's arrival in the secretive state, the U.S. State Department was careful not to raise hopes.

"Obviously, it's a mission to secure the release of Mr. Gomes, but we don't want to jeopardize the prospect for Mr. Gomes to be returned home by discussing any of the details," a State Department spokesman said.

Gomes was an English teacher in South Korea and a devout Christian who is said to have been on a self-appointed peace mission. Last month North Korean officials notified U.S. representatives that Gomes had tried to commit suicide.

North Korea is also willing to resume six-party nuclear disarmament talks and denuclearization of the Korean peninsula through Carter, state media said.

A successful precedent for Carter's mission is former President Bill Clinton's visit last year. That trip resulted in the pardon and release of two U.S. journalists, also accused of illegally entering North Korea.

Carter was expected to leave Thursday, but he extended his stay.

He may not have met with ailing North Korean leader Kim Jong Il. South Korean media confirmed that Kim unexpectedly left by train bound for China, the second trip for him in a year.

Neither North Korea nor China ever officially announce a visit by Kim until he is back in Pyongyang.

Kim's visit to China may be to discuss with Chinese leaders his succession plans, which most analysts have predicted will place at the helm of the secretive communist state his third son, Kim Jong Un, 27, believed to be with his father in China.

Kim's visit comes just before the North Korea's ruling communist Workers' Party of Korea will have a meeting of its central political bureau "for electing its highest leading body" next month.

Analysts believed the extraordinary meeting when announced in June was a signal that Kim may be getting ready to take a back seat in favor of his son, who he has been grooming for higher office for several years.

Last year there was speculation that the Swiss-educated Kim Jong Un was already leading the Workers Party of Korea as part of his eventual rise to replace his father.

Kim Jong Un reportedly attended the English-language International School of Bern under a false name in 1998, and few photographs of him exist.

His father, Kim Jong Il, took power in 1994 upon the death of his father, Kim Il Sung, a devoted communist who ruled North Korea from its founding in 1948. But the current leader is said to have suffered a severe stroke in 2008 and he may have some form of cancer.