The Richardson-Schmidt trip comes at a delicate time politically. In December, North Korea defiantly shot a satellite into space on the back of a three-stage rocket last month, a launch Pyongyang has hailed as a major step in its quest for peaceful exploration of space.

Washington and others, however, decry it as a covert test of long-range ballistic missile technology designed to send a nuclear-tipped warhead as far as California. The U.N. Security Council quickly condemned the launch, and is deliberating whether to further punish Pyongyang for violating bans on developing its nuclear and missile programs.

The visit also follows North Korea's announcement that an American citizen of Korean descent has been jailed in Pyongyang on suspicion of committing "hostile" acts against the state. Conviction could draw a sentence of 10 years of hard labor under North Korea's penal code.

Kenneth Bae, identified in North Korean state media by his Korean name, Pae Jun Ho, is the fifth American detained in North Korea in the past four years. The exact circumstances of his arrest were not clear. The Korean Central News Agency said he was taken into custody in Rason, a special economic zone in the far north near China and Russia, while touring the area.

Richardson, a former U.S. ambassador to the United Nations who often serves as an envoy to countries that do not have diplomatic relations with the United States, will try to meet with North Korean officials, and possibly Bae, to discuss the case, the sources said.

Richardson has been to North Korea at least a half-dozen times since 1994, including two trips to negotiate the release of Americans detained by North Korea. His last visit to Pyongyang was in 2010.

Also leading the trip is Kun "Tony" Namkung, an Asian affairs expert who has made numerous visits to North Korea over the past 25 years. Namkung also has been a consultant to the AP.

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