The U.S. military will face a difficult task in identifying the remains of soldiers missing from the Korean War as the Pentagon prepares to receive them from North Korea in the coming days, officials and experts said.

U.S. President Donald Trump, who met with North Korean leader Kim Jong Un in Singapore this month, said on Thursday that Pyongyang was in the process of returning the remains of U.S. troops missing from the 1950-1953 conflict.

The Pentagon has said North Korean officials have indicated in the past they have the remains of as many as 200 U.S. troops, and Trump himself has mentioned that figure.