North Korea has expanded a key long-range missile base in the months since a summit between the country's leader Kim Jong-un and US President Donald Trump, according to satellite images published by CNN on Wednesday.
The two men met in Singapore in June and signed a vaguely worded document that pledged to "work toward" the complete denuclearization of the Korean peninsula, though it did not detail specifics on how this would come about.
Experts told the US news network that the site's location made it suitable to host North Korea's newest long-range missiles, including ones that could carry nuclear warheads.
US officials insist on the complete, verified and irreversible denuclearization of the Korean peninsula before tough sanctions are lifted.
But the North has rejected demands for what it calls "unilateral" disarmament and has instead sought unspecified reciprocal US measures in a gradual process.
(With inputs from agencies.)