"Both sides agreed to re-commence field operations in the DPRK to search for the estimated 5,300 Americans who never returned home", Pompeo said.
US President Donald Trump holds up a document signed by him and North Korea's leader Kim Jong Un following a signing ceremony during their historic US-North Korea summit, at the Capella Hotel on Sentosa island in Singapore on June 12, 2018.
South Korea's Yonhap news agency, citing South Korean government sources, said negotiations began on Sunday at the border village of Panmunjom in the so-called Demilitarized Zone (DMZ) separating the two Koreas.
But the process has been slow, with the North Koreans keeping the US -led United Nations Command on standby for weeks after the military sent dozens of temporary coffins to the DMZ in preparation.
"They threatened that unless I went to the South with the staff they would inform the North Korean Embassy that I had been cooperating with the intelligence services", he said.
Since taking power when his dictator father Kim Jong Il died in late 2011, Kim, 34, has promised to boost living standards and sought to project an image of youth and modernity while pushing hard to build up North Korea's nuclear capabilities.
Official U.S. statistics show that 7,699 American personnel remain unaccounted for following the 1950-53 conflict.
"We understand that the North-US talks on repatriation of the remains are underway", it quoted an unnamed official as saying.More news: New Report Reveals What Raptors Offered Spurs For Kawhi Leonard
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A UNC official said he had no information to confirm the report, though preparations had been made for Sunday's talks.
Among the missing foreign soldiers who are believed to have died in the conflict, around 165 were part of the Turkish Brigade, which supplied almost 15,000 troops to fight on the South's side during the war.
At last month's summit meeting Kim made a vague commitment to "work toward denuclearization" but there were no details as to how or when such disarmament would take place.
Citing an unnamed USA official, CNN reported that the US and the North were working to repatriate the remains of some 200 American troops in two to three weeks. But what, if anything, North Korea may be willing to hand over remains unclear.
Putting aside the fact that the Korean War is technically still happening for a moment, this agreement still marks yet another major step towards peace in Korea.
In addition to the announcement on joint searches, the U.S. 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 United States official told CNN.
"A very nice note from Chairman Kim of North Korea", Trump tweeted alongside a copy of the letter.
Pompeo had hoped to "fill in" details on how to dismantle the North's nuclear program and recover the remains of US troops in his talks in Pyongyang this month.