North Korea turned over what are believed to be the remains of 55 U.S. service members who were killed during the Korean War of the 1950s on Friday local time, the 65th anniversary of the armistice that ended the fighting, the United States and the United Nations said.

A U.S. cargo aircraft flew to Wonson, North Korea, to receive the remains and returned to Osan Air Base, South Korea, the unified U.N. Command for Korea and U.S. Forces Korea said in a statement.

U.S. service members carry boxes out of the C-17 Globemaster at Osan Air Base in Pyeongtaek, about 70 kilometers south of Seoul, South Korea, on July 27, 2018. Yonhap / Pool via EPA

"It was a successful mission following extensive coordination,” said U.S. Army Gen. Vincent K. Brooks, commander of both structures. "Now, we will prepare to honor our fallen before they continue on their journey home."

U.S. servicemen and women, joined by a military honor guard, lined up on the tarmac at Osan to receive the remains, which were carried in boxes covered in blue U.N. flags, according to The Associated Press. Brooks will host a full honors ceremony next Wednesday, the combined command said.

The remains were accompanied by technical experts from the Defense POW/MIA Accounting Agency, the White House said.

The return is part of an agreement reached during the June summit between President Donald Trump and North Korean leader Kim Jong Un. The transfer sets off a lengthy series of forensic examinations and tests to determine whether the remains are human and whether they are actually U.S. or allied troops who were killed in the conflict.

Referring to Kim, the White House said in a statement: "Today, the chairman is fulfilling part of the commitment he made to the president to return our fallen American service members.

"We are encouraged by North Korea's actions and the momentum for positive change," it said.

Trump said on Twitter Thursday night: "After so many years, this will be a great moment for so many families. Thank you to Kim Jong Un."

About 7,800 U.S. service members were lost and unrecovered from the Korean War, and about 5,300 of those were lost in North Korea, according to the Defense Department. The war, which was fought from June 25, 1950, until July 27, 1953, is sometimes referred to as "The Forgotten War."

Joint U.S.-North Korea military search teams collected 229 sets of U.S. remains from 1996 to 2005. But efforts to recover and return more remains stalled for more than a decade as Washington and Pyongyang clashed over North Korea's nuclear weapons program. The United States, meanwhile, alleged that the safety of its recovery teams wasn't being guaranteed.

South Korea President Moon Jae-in said Wednesday during a meeting with Harry Harris, the new U.S. ambassador to Seoul, that the transfer of the remains would boost momentum for talks on the North's nuclear program.