In a pair of overnight tweets, President Trump sent his thanks early Thursday to North Korean leader Kim Jong Un for returning 55 boxes presumed to contain the remains of Americans who served in the Korean War.

"Thank you to Chairman Kim Jong Un for keeping your word & starting the process of sending home the remains of our great and beloved missing fallen!" Trump wrote in one tweet. "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!"

The return of the remains was part of an agreement reached by Trump and Kim during a June summit in Singapore.

North Korea handed over the remains last week. A U.S. military plane made a rare trip into North Korea to retrieve the 55 cases.

Hundreds of U.S. and South Korean troops gathered for a repatriation ceremony at the Osan base in South Korea before the cases were put on military planes bound for Hawaii.

On Wednesday, Vice President Mike Pence and the top commander of U.S. forces in Asia, Navy Adm. Phil Davidson, formally received the remains during the emotional and solemn ceremony in Hawaii.

Pence spoke during a ceremony at Hawaii's Hickam Air Force Base to mark the arrival of the remains on U.S. soil and the beginning of the long process of identifying them.

"They were husbands and fathers, brothers and neighbors — long gone, but never lost to the memory of their loved ones." — Mike Pence, U.S. Vice President

"They were husbands and fathers, brothers and neighbors — long gone, but never lost to the memory of their loved ones," Pence said.

Some of the invited guests wiped tears from their eyes during the procession.

Trump lauded Pence and the ceremony in an earlier tweet.

"Incredibly beautiful ceremony as U.S. Korean War remains are returned to American soil. Thank you to Honolulu and all of our great Military participants on a job well done," Trump tweeted late Wednesday night. "A special thanks to Vice President Mike Pence on delivering a truly magnificent tribute!"

Pence also said Trump was grateful Kim kept his word.

"We see today as tangible progress in our efforts to achieve peace on the Korean Peninsula," the vice president said.

Defense Secretary Jim Mattis said last week that the return of the 55 cases was a positive step but not a guarantee that the bones are American soldiers.

At the repatriation ceremony in South Korea, the cases were draped in United Nations flags in a possible sign of that uncertainty. On Wednesday, however, the cases were draped in U.S. flags.

NORTH KOREA RETURNED 1 DOG TAG WITH 55 SETS OF SOLDIER REMAINS, US OFFICIAL SAYS

Nearly 7,700 U.S. service members were listed as missing and unaccounted for from the 1950-53 Korean War. The Pentagon estimates that of the approximately 7,700 U.S. MIAs from the Korean War, about 5,300 are unaccounted for on North Korean soil.

The Defense POW/MIA Accounting Agency will take the remains to a lab on the base where forensic anthropologists will study bones and teeth to identify their race, gender and age. Scientists will extract DNA and compare it to DNA samples collected from families of troops still missing from the war.

It could take months or years to determine their identities.

"(T)his is an international effort to bring closure for those families." — Jim Mattis, U.S. Defense Secretary

"(T)his is an international effort to bring closure for those families," Mattis had said.

The Associated Press and Fox News' Samuel Chamberlain contributed to this report.