North Korea repatriated on Friday morning what appears to be 55 sets of remains from U.S. troops killed in the Korean War, prompting President Donald Trump to personally thank North Korean dictator Kim Jong-un on Twitter.

Trump issued his tweet of gratitude as the remains were departing North Korea on Thursday night:

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

The White House issued a statement on Thursday noting that the return of Korean War dead was one of the issues President Trump discussed with Kim Jong-un during their summit in Singapore:

A U.S. Air Force C-17 aircraft containing remains of fallen service members has departed Wonsan, North Korea. It is accompanied by service members from United Nations Command Korea and technical experts from the Defense POW/MIA Accounting Agency. The C-17 is transferring the remains to Osan Air Base, where a formal repatriation ceremony will be held on August 1. The United States owes a profound debt of gratitude to those American service members who gave their lives in service to their country and we are working diligently to bring them home. It is 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. Today’s actions represent a significant first step to recommence the repatriation of remains from North Korea and to resume field operations in North Korea to search for the estimated 5,300 Americans who have not yet returned home.

Honor guards from nations that served under U.N. command during the Korean War met the remains at Osan Air Base. “White-gloved troops in different uniforms descended the ramp of the US Air Force C-17, carefully holding cases wrapped in the UN flag. The cases were transferred to silver minivans waiting on the runway,” CNN reported Friday morning.

“It was a successful mission following extensive coordination. Now, we will prepare to honor our fallen before they continue on their journey home,” said General Vincent K. Brooks, commander of U.S. Forces Korea.

The long process of verifying the remains is now underway, with everything from DNA to dog tags and uniform fragments carefully examined by forensic technicians. The work will reportedly be undertaken at a U.S. military laboratory in Hawaii. A formal repatriation ceremony is scheduled for Wednesday in Osan before the remains are flown to Hawaii.

The last repatriation of U.S. remains from North Korea took place in 2007, following a ten-year joint project to locate and verify American war dead. About 7,700 American troops from the Korean War remain unaccounted for. North Korea is believed to be holding at least 200 sets of remains in storage, ready to deliver whenever the dictatorship sees fit.

Friday is the 65th anniversary of the armistice that effectively ended the Korean War, although no peace treaty was ever signed. North Korean media said little about the repatriation of American remains, instead focusing on ceremonies at memorials for North Korean and Chinese war dead.

Kim himself was photographed at a statue of a North Korean soldier, where he reportedly said, “The Korean people would as ever take pride in having the creditable fraternal country and the great friend like the People’s Republic of China.” Kim also laid a wreath at the “Fatherland Liberation War Martyrs Cemetery” and met with North Korean war veterans.

The possibility of formally ending the Korean War with a peace treaty has been floated by U.S. and South Korean officials as diplomatic relations with North Korea thawed. Pyongyang is now suspiciously eager to get treaty talks underway because they believe it would weaken international sanctions and the American military presence in South Korea, as the Japan Times reported Friday:

Post Kim-Trump summit talks between U.S. 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 U.S. officials came up with various “conditions and excuses” to backtrack on the issue of formally ending the war. “The adoption of the declaration on the termination of war is the first and foremost process in the light of ending the extreme hostility and establishing new relations between the DPRK and the U.S.,” the North’s Korean Central News Agency said in a statement on Tuesday, referring to North Korea by its official name, the Democratic People’s Republic of Korea. “Peace can come only after the declaration of the termination of war.” Pompeo said Wednesday that a great deal of work remains ahead of a North Korea denuclearization deal, but he dodged requests to identify a specific denuclearization timeline in testimony to members of the Senate Foreign Relations Committee. Experts say a declaration to officially end the war, which could also involve Seoul and Beijing, would make it easier for Pyongyang to steer the discussions with Washington toward a peace treaty, diplomatic recognition, security assurance and economic benefits. Some analysts believe that North Korea would eventually demand that the United States withdraw or dramatically reduce the 28,500 troops it keeps in South Korea as a deterrent.

The Trump administration has welcomed gestures such as the return of the Korean War dead and the apparent dismantling of some North Korean missile facilities but continue to insist that full denuclearization must be achieved before sanctions will be lifted. It remains to be seen if anything less than full denuclearization would be sufficient to allow talks on a Korean War peace treaty, especially given North Korea’s obvious interest in using such talks to weaken the sanctions regime.

Update: Secretary of Defense Jim Mattis clarified on Friday afternoon that the remains returned by North Korea may not be entirely American. Pointing to the U.N. flags draped over the containers holding the remains, Mattis said, “We don’t know who is in those boxes. As we discover it, we will return them. They could go to Australia – they have missing. France has missing. America has missing.”