OSAN AIR BASE, South ­Korea — M ore than 60 years after the last shot was fired in the Korean War, the U.S. military prepared Wednesday to fly home what are believed to be the remains of more than 50 service members after the first such handover by North Korea in more than a decade.

North Korea transferred the remains last week, the first tangible moves from agreements reached between President Trump and North Korean leader Kim Jong Un at their meeting in Singapore on June 12.

After a solemn ceremony at the U.S. military’s Osan Air Base in South Korea, 55 boxes of remains draped in the United Nations flag were taken to a pair of U.S. military planes, which flew them to a military laboratory in Hawaii for analysis and identification.

Initial forensic analysis suggested that the remains were likely to be those of American service members, the U.S. military said. But experts say positive identification of all the remains could take years.

“Generally speaking, what I can tell you is that the remains are consistent with the remains we have recovered in North Korea,” John Byrd, director of analysis for the U.S. Defense POW/MIA Accounting Agency, told a news conference before the ceremony.

Byrd said the preliminary findings of the U.S. investigation were that the remains are what North Korean officials said they are. 

“They are likely to be American remains,” he said.

Vice President Pence, who was on hand at Joint Base Pearl Harbor-Hickam in Hawaii to receive the remains in an honorable carry ceremony, said, “To these great American heroes fallen so long ago, today as a nation we breathe a word of thanks for your service and sacrifice and we say to you, as one people with one voice, welcome home.”

Uniformed personnel carried the caskets, covered now by American flags, off the planes and set them inside a hangar as a military band played taps and Pence joined commanders standing at attention.

Pence hailed the moment has a breakthrough after more than a decade in which no remains were handed over by Pyongyang amid a deepening standoff between the nations over North Korea’s nuclear weapons program. The Trump White House has sought to maintain momentum after Trump’s summit with Kim, during which the two sides agreed to accelerate efforts to return the fallen troops as a trust-building measure.

“What we see today is tangible progress in our efforts to keep peace on the Korean Peninsula. But today is just the beginning,” said Pence, whose father was a Korean War veteran. “Our work will not be complete until all our fallen heroes are accounted for and home. We will see to it in the days ahead that these heroes lead the way to many more homecomings in the future.”

Trump thanked Kim in an early morning tweet Thursday, writing “I am not at all surprised that you took this kind action. Also, thank you for your nice letter - l look forward to seeing you soon!”

North Korea provided enough information about where the bodies were found to allow U.S. officials to match them to battles fought in 1950 and 1951, Byrd said.

One dog tag was also returned, and the family of that soldier has been informed, but it has not been established whether his remains were among those returned, Byrd said.

Indeed, North Korean military officials did not claim that all items in each box went together, he said. 

“They expressed concern that there was a lot of co-mingling when these remains were recovered from the very beginning,” he said. “We do hope that the individual whose dog tag that is is somewhere among these remains we’ve taken back, and we will certainly be very aggressive in trying to run that to ground.”

Byrd said a lot of military hardware — such as helmets, canteens and boots — was included in the shipment.

The Pentagon estimates that nearly 7,700 U.S. troops are unaccounted for from the war; among them are 5,300 believed to have been killed north of the 38th parallel, which largely follows the boundary between North and South Korea. Most died on the battlefield and were buried in shallow graves or in cemeteries that were intended to be temporary, but some also perished in POW camps run by North Korea or China, experts say.

The process of finding and repatriating their remains has long been hampered by North Korea’s reluctance to allow U.S. military investigators unrestricted access to battle sites and by the North’s desire to wring as much political capital and money out of the process of returning the remains as possible.

Rick Downes, executive director of a group of families whose loved ones never came home from the Korean War, said it now appears that Pyongyang is trying to help.

“It is especially good to know locations where some of the remains were found,” said Downes, who runs the Coalition of Families of Korean & Cold War POW/MIAs. “This should hasten identifications quite a bit.”

Troops from 16 other nations fought alongside the Americans under the U.N. flag during the Korean War, and diplomats and officials from all those countries placed wreaths at the ceremony. Defense Secretary Jim Mattis said last week it was possible that some of the remains could belong to soldiers from those nations, and if so, they would be repatriated once they have been identified.

On Wednesday, U.S. Consul General Angela Kerwin said that no money was paid to North Korea for the remains. 

The remains were flown from the North Korean city of Wonsan last Friday, on the 65th anniversary of the Korean War armistice, and were greeted at Osan Air Base by hundreds of U.S. service personnel and their families.

Another ceremony was conducted Wednesday as the remains were sent to Hawaii, with bugles playing taps, as well as “The Last Post,” a call used at funerals by British and Commonwealth militaries, and a South Korean bugle call. National anthems of the United States and South Korea were played, and the caskets were given a three-volley salute by U.S. riflemen.

Secretary of State Mike Pompeo said last month that the two sides have agreed to recommence field operations in North Korea to search for missing Americans, and the Pentagon said it is considering sending personnel to North Korea for this purpose.

The United States and North Korean militaries conducted joint searches for missing service members from 1996 until 2005, and 400 caskets of remains were handed over during that period. 

But Washington then halted the program, citing concerns about the safety of its personnel as Pyongyang stepped up its nuclear program. The United States says it does not pay directly for the remains but has given the North Koreans “compensation” for the costs of the recovery in the past.

“Whosoever emerges from these aircraft, so begins a new season of hope for our families of the fallen,” Pence said. “Hope that those who are lost will yet be found. Hope that after so many years of questions, these families will have closure. And hope that, as President Trump said just yesterday, these and others to follow will finally come home and be laid to rest in American soil.”

Denyer reported from Tokyo. David Nakamura in Washington contributed to this report.