(CNN) — Secretary of State Mike Pompeo announced Sunday that the United States and North Korea agreed to recommence field operations to search for the estimated 5,300 Americans who never returned home from the Korean War.

The US and North Korea will jointly engage in the searches for the yet-to-be-located service members’ remains, State Department spokeswoman Heather Nauert confirmed; she could not say when those would begin.

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The joint US-North Korea program to search for remains began in 1996 but was suspended in 2005 due to rising nuclear tensions.

Pompeo called the talks over the weekend that led to the announcement “productive, cooperative and resulted in firm commitments.”

In addition to the announcement on joint searches, the US and North Korea are working to transfer the remains of what could be 200 American service members in the 14 to 21 days “subject to change without notification,” a US official told CNN.

US officials have previously said it could take years to identify all the remains and to determine whether they are, in fact, Americans.

“Working level meetings between U.S. and North Korean officials will begin” Monday to coordinate the next steps, including the transfer of remains already collected by North Korea, Pompeo said in a statement.

Trump has touted the planned return of remains as one of the successes of his historic June 12 summit with North Korean leader Kim Jong Un.

CNN reported last month that the Trump administration was expecting North Korea to return the US troop remains and that planning for the exchange has been underway. About 100 wooden transport cases were sent to the demilitarized zone in recent weeks to prepare for receiving the remains.

On Sunday, President Donald Trump tweeted about what he considered successes in the US-North Korea talks so far.

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“There hasn’t been a missile or rocket fired in 9 months in North Korea, there have been no nuclear tests and we got back our hostages,” Trump wrote. “Who knows how it will all turn out in the end, but why isn’t the Fake News talking about these wonderful facts?”

North Korean officials did not show up to a planned meeting with US officials at the demilitarized zone Thursday, where they were expected to continue discussions on repatriating the remains of Americans killed during the war, CNN has reported.

The no-show came after Kim scuttled a rendezvous with Pompeo during his trip to Pyongyang earlier this month.

READ: What happened the last time Pompeo met with North Korea

Pompeo did not demonstrate progress on denuclearization talks after that trip, leading one source with knowledge of the discussions to say the White House felt it went “as badly as it could have gone,” CNN reported.

The developments fueled skepticism over North Korea’s commitment to the complete denuclearization of the Korean Peninsula as promised during last month’s meeting between Trump and Kim in Singapore.

But last week, Trump insisted “great progress” was being made in the talks, releasing a praise-filled letter from Kim dated July 6, the start of those talks, that was given to Pompeo’s delegation to deliver.

In the letter, Kim wrote, “I firmly believe that the strong will, sincere efforts and unique approach of myself and Your Excellency Mr. President aimed at opening up a new future between the DPRK and the US will surely come to fruition.”

Kim also said the Singapore summit and the letter both leaders signed during that meeting were “indeed the start of a meaningful journey.”

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