U.S. presidential candidate and New Mexico governor Bill Richardson, fifth from left, poses with his delegation on arrival Sunday at an airport in Pyongyang, North Korea. Richardson, who has undertaken diplomatic missions to countries at odds with the United States, is visiting isolated North Korea to recover remains of American servicemen killed in the Korean war. The four-day trip that started Sunday with the endorsement of the administration of U.S. President George W. Bush comes days before a crucial deadline in a recent nuclear disarmament accord.

Pyongyang, North Korea ? Bill Richardson, the New Mexico governor who has undertaken diplomatic missions to countries at odds with the United States, began a rare visit to isolated North Korea Sunday to recover remains of American servicemen killed in the Korean War.

The four-day trip, which has been endorsed by the Bush administration, comes days before a crucial deadline in a recent nuclear disarmament accord. But Richardson, a Democratic candidate for president, said he had no intention of negotiating nuclear matters.

“It could be the signal of an improved relationship,” Richardson said of the discussions to secure U.S. remains. “The North Koreans always consider protocol very important. They like to be considered a major power in the region,” he told The Associated Press on the flight to the capital Pyongyang.

North Korea made a breakthrough agreement on nuclear disarmament on Feb. 13, raising hopes for an end to a long-running standoff with the United States and regional powers. The agreement set an April 14 deadline for the North to shut down its main nuclear reactor.

Despite the breakthrough nuclear agreement in February, there has been little progress since. The impoverished North has refused further negotiations due to the delayed transfer of $25 million in the regime’s money frozen by Macau authorities after the U.S. blacklisted a bank in that Chinese administrative region in 2005 for allegedly helping Pyongyang launder money.

Some worry that delay could hold up implementation of the disarmament agreement.

The State Department said Friday that a hitch stalling the release of the funds had been resolved, potentially clearing the way for the disbursement of the money. No details were released on when or how the money would be transferred.

North Korea’s defense minister praised the country’s nuclear program on Sunday at a meeting of top officials and said the North had achieved status as a nuclear power.

North Korea “has legitimately ranked itself among the nuclear weapons states,” Vice Marshal Kim Il Chol said, according to a report from the official Korean Central News Agency.

Richardson has regularly made diplomatic trips, often on his own initiative, to a number of global hot spots. Though visits to North Korea by senior U.S. officials are rare, this was Richardson’s sixth.

A former U.S. ambassador to the United Nations and energy secretary in the Clinton administration, Richardson also visited Sudan in January to try to end four years of fighting in the Darfur region.

Richardson said the timing of his visit is important and will show North Korea the United States’ good intentions. He said the North Koreans will understand the symbolism of a delegation that includes Anthony Principi, Bush’s former veteran affairs secretary, and Victor Cha, a top adviser on North Korea.

His group is expected to oversee the transfer of remains from the North Korean army to U.N. personnel.

More than 33,000 American troops died in the Korean War from 1950-1953, and more than 8,100 are listed as missing. After North Korea invaded South Korea, U.S. forces intervened on behalf of the South while Chinese forces backed the North.