If they were to happen, either of the trips would mark a significant shift in US-North Korea relations, particularly after the bellicose rhetoric the two leaders exchanged in 2017.
U.S. vice president Mike Pence spoke at a ceremony before the flag-draped containers carrying the remains were taken off planes in sets of four.
"However, the attitude and stance the United States showed in the first high-level meeting (between the countries) was no doubt regrettable", the spokesman said.
The U.S. State Department said on Tuesday it expects Pyongyang to keep its commitment made at the June summit to give up its nuclear arms which it had developed for years in defiance of U.N. Security Council sanctions.
"Our science has also improved exponentially in recent years, so our DNA analysts can now make a more complete identification with less DNA", she said, "which does help offset the age of some of the remains". But there have been worries that North Korea hasn't since taken any serious disarmament measures.
North Korea is one of 27 members of the forum, which in the past has served as a venue for meetings between top diplomats from Pyongyang and Washington.
The remains will be examined at the Defense POW/MIA Accounting Agency, and experts there will be responsible for identifying the remains.
The recovery efforts stalled for more than a decade because of a standoff over North Korea's nuclear ambitions and a previous USA claim that security arrangements for its personnel working in the North were insufficient. Some of them, including Australia, Belgium, France and the Philippines, are yet to recover some of their war dead from North Korea.
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The charges against Manafort largely pre-date his five months of work for the Trump campaign, some of them as campaign chairman. Manafort", the elder Katzman said of a picture of the brown leather jacket that the feds entered into evidence Wednesday.
Before the remains were put on military planes bound for Hawaii, hundreds of US and South Korean troops gathered at a hanger at the Osan base in South Korean for the repatriation ceremony.
Gen. Kim Do Gyun said he's confident the talks would produce "achievements that South and North Korea and the global community want", according to South Korean media pool reports from the venue.
A number of USA war dead are believed to be buried in mass graves in North Korea, not far from the border with the South.
The remains were then moved in grey vans to an airfield where US and South Korean soldiers loaded them one by one into transport planes. Trump thanked Kim for the return.
Still, the initial field forensic review indicated the "remains are what North Korea said they were", Byrd said.
North Korea's intention was to deceive the U.S.by misconstruing the number of warheads as well as research facilities they have, while claiming they have fully denuclearised, the Post reported, citing intelligence.
But many experts say those are neither irrevocable nor serious steps that could show the country is honest about denuclearisation.
The returns of f dozens of servicemen who were killed in the Korean War. The two sides remain technically at war because a peace treaty was never signed.