A U.S. military plane left North Korea on Thursday carrying the remains of U.S. troops killed decades ago in the Korean War, the White House said.

The Air Force C-17 aircraft left the coastal city of Wonsan en route to Osan Air Base in South Korea, roughy 43 miles south of Seoul, White House press secretary Sarah Huckabee Sanders said in a statement.

A formal repatriation ceremony is set to be held on Aug. 1.

The caskets coming out pic.twitter.com/pEDmHQKVM4 — Adam Taylor (@mradamtaylor) July 27, 2018

The United Nations Command said 55 cases of remains were retrieved, according to The Associated Press.

President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE touted the return as "a great moment for so many families."

"Thank you to Kim Jong Un," he tweeted.

The Remains of American Servicemen will soon be leaving North Korea and heading to the United States! After so many years, this will be a great moment for so many families. Thank you to Kim Jong Un. — Donald J. Trump (@realDonaldTrump) July 27, 2018

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The repatriation of the remains comes as part of a deal struck by Trump and North Korean leader Kim Jong Un during a landmark summit in Singapore last month.

While the fighting in the Korean War lasted from 1950 until 1953, the war never formally ended because a treaty was never signed.

There about an estimated 5,300 Americans who did not return home from the conflict.

CNN reported on Tuesday that the U.S. had not yet received confirmation from the North that the remains would be returned, and that Pyongyang had not given either the U.S. or South Korea the go-ahead for the transfer.

But Yonhap reported Thursday that the North would begin returning the remains.

Trump had previously said that the North had already returned the remains of about 200 service members.

At a speech in Kansas City, Mo., on Tuesday, he walked back his comments, suggesting instead that the process was just starting.

"I hope that, very soon, these fallen warriors will begin coming home to lay at rest in American soil," Trump said. "That’s starting the process."

Updated July 27 at 6:12 a.m.