U.S. envoys made a rare crossing Wednesday of the border dividing the two Koreas with the remains of six American soldiers from the Korean War, completing a mission where they pushed for action on North Korea 's nuclear disarmament.

New Mexico Gov. Bill Richardson and former Veterans Affairs Secretary Anthony Principi were greeted at the frontier between North and South by U.S. Ambassador to South Korea Alexander Vershbow and U.S. military officials.

Richardson spent four days in North Korea, also joined by the top White House adviser on Korea, Victor Cha.

• Monitor the nuclear showdown on the Korean Peninsula in FOXNews.com's North Korea Center.

"Hopefully, we've done our bit to relieve the tension between our two countries," Richardson said after crossing the border, referring to the U.S. and the North.

While in the North, the delegation met with officials to press Pyongyang to meet a Saturday deadline to shut down its sole operating nuclear reactor under a February agreement with the U.S. and other regional powers.

It's unclear if the deadline will be met due to a separate dispute over frozen North Korean funds that Pyongyang has insisted be resolved before it moves to disarm.

Authorities in the Chinese territory of Macau, where North Korea had its accounts, said Wednesday that the money is now free for withdrawal. North Korea has yet to say whether it is satisfied with the resolution of the issue.

On Wednesday, the Americans drove two hours from the North Korean capital, Pyongyang, with the remains of the soldiers transported separately in small, black cases.

They then walked across the North-South frontier at the truce village of Panmunjeom, where the two Koreas stand face-to-face across the border that has divided the peninsula since a 1953 cease-fire ended the Korean War.

Principi said the mission to deliver the remains was one of the most emotional moments of his life.

"To participate in such a noble mission to bring home the remains of men who 50 years ago were in harm's way, and now they're home, it was really quite moving," he said.

More than 33,000 U.S. troops died in the Korean War, which began in June 1950 when North Korea invaded South Korea. Some 8,100 U.S. servicemen are still listed as missing.

In 2005, the U.S. government halted a separate cooperative program that permitted U.S. military teams to excavate remains from North Korean battlefields, saying the North had created an unsafe environment. The program had recovered remains believed to be from 220 soldiers since 1996.

Later Wednesday, Richardson was to meet with South Korean diplomats before departing Thursday to Hawaii.

Complete coverage is available in FOXNews.com's North Korea Center.