The White House said it was "encouraged" by the return of the remains and the "momentum for positive change".
Donald Trump and Kim Jong Un's historic summit in pictures Who's leading whom?
The U.S. State Department says Washington is committed to building a peace mechanism to replace the armistice when North Korea has denuclearised.
The White House said it was "a solemn obligation of the United States Government to ensure that the remains are handled with dignity and properly accounted for so their families receive them in an honorable manner". Chris Murphy's tough questioning on whether North Korea agreed to the U.S. definition of denuclearization, Secretary of State Mike Pompeo affirmed that the North Koreans agreed to denuclearize according to a USA definition of denuclearization that was "not dissimilar to how the United Nations has characterized it, [or] how South Koreans have characterized it".
Efforts to recover American war dead had been stalled for more than a decade because of a standoff over North Korea's nuclear program and a previous USA claim that security arrangements for its personnel working in the North were insufficient. "It's an honor to bring the remains home", he said, adding that the case he carried weighed about 15 pounds.
The move was first reported by South Korea-based Yonhap news agency.
It is believed that 55 soldiers have been returned this time but their remains will need to be forensically tested to ensure they are indeed slain U.S. troops - it's possible that the identification process could take years.More news: Was it legal for Michael Cohen to secretly tape Trump?
The handover is the result of an agreement between President Donald Trump and North Korean leader Kim Jong Un at a June 12 summit. The two leaders also agreed to build a "robust peace regime" and to return the remains of prisoners of the 1950-1953 Korean War.
Efforts to recover American war dead had been stalled for more than a decade because of a standoff over North Korea's nuclear program and a previous United States claim that security arrangements for its personnel working in the North were insufficient.
At the very minimum, it will take meeting, talking, building trust and having a working relationship to convince North Korea - which was destroyed by U.S. warplanes during the Korean War - to give up its sole deterrent to prevent an American nuclear first strike.
From 1996 to 2005, joint US-North Korea military search teams conducted 33 recovery operations that collected 229 sets of American remains.
July 27 marks the 65 anniversary of the Armistice Agreement when the US, North Korea and China signed a ceasefire to halt three years of brutal fighting which claimed 4 million lives. Although family reunions are planned between North Korea and South Korea on August 15, 2018, Korean American families have yet to be included in such a lottery.
Post Kim-Trump summit talks between US Secretary of State Mike Pompeo and senior North Korean officials got off to a rocky start earlier this month, with the North accusing the Americans of making "unilateral and gangster-like" demands on denuclearization. The North also said US officials came up with various "conditions and excuses" to backtrack on the issue of formally ending the war. Though the U.S. is a major belligerent within the Korean War, and would be needed for peace, being the lone holdout would be seriously embarrassing. Earlier, the plane and its crew had traveled to Wonsan, North Korea, to collect the remains, the White House said.
South Korea welcomed the return of the remains, calling it "meaningful progress that could contribute to fostering trust" between Pyongyang and Washington. North Korean leaders will not give up their nuclear program unless they have hard assurances in the form of a peace agreement that the United States won't attack their country. In exchange, Trump agreed to provide "security guarantees" to Pyongyang.