US President Donald Trump thanked North Korean leader Kim Jong-un Friday for "keeping his word" and returning the remains of American troops killed in the 1950-53 Korean War.

Boxes of the remains were airlifted from North Korea to South Korea the same day in line with a pledge Kim made at his historic summit with Trump in Singapore last month.

Speaking to reporters outside the White House, Trump said he hoped the North Korean leader will "continue to fulfill that promise" through the recovery and repatriation of more remains.

"At this moment a plane is carrying the remains of some great fallen heroes from America back from the Korean War," Trump said.

"They're coming back to the United States. Mike Pence, our wonderful vice president, will be there to greet the families and the remains."

A US Air Force aircraft transported 55 sets of remains to Osan Air Base, south of Seoul, where they will be honored in a ceremony Wednesday. The remains will then be sent to a forensic lab in Hawaii the same day.

"I want to thank Chairman Kim for keeping his word," Trump said. "We have many others coming. But I want to thank Chairman Kim in front of the media for fulfilling a promise that he made to me and I'm sure that he will continue to fulfill that promise as they search and search and search. These incredible American heroes will soon lay at rest on sacred American soil."

The repatriation took on symbolic meaning as it coincided with the anniversary of the signing of the Armistice Agreement that ended the Korean War. The remains of an estimated 5,300 American soldiers have yet to be recovered in North Korea.

Defense Secretary Jim Mattis told reporters at the Pentagon that US personnel could be sent to North Korea to assist in the search effort.

He also noted that North Korea's action Friday set a "positive tone" for the two countries' engagement on other issues, including Washington's push to dismantle Pyongyang's nuclear weapons program as part of the summit agreement.

US Secretary of State Mike Pompeo also expressed his appreciation to the North Korean leader, whom he has met at least three times as Washington's point man on negotiations with Pyongyang.

"At his meeting with @POTUS, Chairman Kim made a commitment to repatriate the remains of American POW/MIAs," Pompeo tweeted. "I'm pleased he is following through on that commitment."

Pence acknowledged that he was asked by Trump to attend the ceremony in Hawaii Wednesday.

"As the son of a Korean War combat veteran, it is deeply humbling to be part of this historic moment," he said in a statement. "We will never forget the sacrifices these brave service members and their families made for our nation and our freedoms."

Pence's father, Edward, received the Bronze Star Medal in 1953 for his service during the war. (Yonhap)