"It takes anywhere from a few months to, in many cases, years, before we can make an identification", Kelly McKeague, head of the USA agency that tracks down remains of USA soldiers lost on foreign battlefields, said in an interview.
Kim Jong-un, the North Korean leader, appears to have opted to visit a potato farm instead of meeting Mike Pompeo when the US Secretary of State was in Pyongyang over the weekend for the latest round of discussions on the future of the Korean Peninsula.
However, officials say it could be months before excavations can begin and years until the remains are identified.
Pompeo said after his trip that there had been progress in the talks.
The meeting came only weeks after Kim pledged to "denuclearise" his country at a summit in Singapore with Donald Trump.
After the summit, Trump said Pyongyang had already "sent back" the remains of 200 US troops. Kim Jong-un vowed to push forward with the "complete denuclearization of the Korean Peninsula" in a statement signed alongside President Trump, but never clarified what that statement meant. US investigators collected a further 230 boxes of bones and material in a decade of digging.
It would be the first such repatriation in more than a decade after a joint search effort was halted amid rising tensions over the North's nuclear weapons program.
The two sides had been expected to discuss at the Korean Peninsula's demilitarized zone the return of US troop remains from the 1950-1953 war - an arrangement that the State Department had announced after Secretary Mike Pompeo's visit to Pyongyang last Friday and Saturday.
Latest Round of Proposed Chinese Tariffs Includes Flooring
The United States complained China used predatory practices in a push to challenge American technological dominance. Beijing's lopsided trade balance with the United States means it will quickly run out of imports for retaliation.
McKeague said no new remains had been returned since the Trump-Kim talks.
"Denuclearization will be next used as a bargaining chip and guarantee for North Korea to negotiate for [future] economic incomes". Leaders from North Atlantic Treaty Organisation member and partner states are meeting for a two-day summit, which is being overshadowed by strong demands by U.S. President Trump for most North Atlantic Treaty Organisation member countries to spend more on defense.
Trump later added on Twitter that the decision would "save a fortune". The U.S. was also supposed to receive the remains of servicemen killed in the Korean War of the early 1950s.
The Trump administration's latest announcement to slap tariffs on an extra $200 billion of Chinese imports has sparked an outcry from China, whose commerce ministry said on Wednesday the US move is "unacceptable" and hurts America's own interests, China and the rest of the world.
What Pyongyang really wants is a four-party meeting with South Korea, China and the United States, the professor said.
A spokesman for U.S. Forces Korea referred questions Thursday to the Department of Defense in Washington.
Trump told reporters Tuesday that he might have another gift for Kim as well.