(CNN) North Korea appears to be finalizing the expansion of a key ballistic missile manufacturing site, according to an analysis of satellite imagery by researchers in the United States.

The images come as leaked reports from US intelligence officials appear to cast doubt on North Korea's willingness abandon its nuclear weapons program, something Washington said North Korean leader Kim Jong Un agreed to when he met US President Donald Trump in Singapore last month.

The satellite images, taken by San Francisco-based Planet Labs Inc. and analyzed by researchers at the Middlebury Institute for International Studies (MIIS) in Monterrey, show Pyongyang finishing construction at the Chemical Material Institute, which researchers say is based in the North Korean city of Hamhung.

The Chemical Material Institute is known for making carbon composite parts for solid-fueled missiles like nozzles, airframes and nosecones used in re-entry vehicles, according to David Schmerler, a research associate at MIIS.

"The Chemical Materials Institute seems like they have one function, and that's pumping out parts for their missile program," Schmerler said.

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