American spy agencies have said there were indicators that showed North Korea was constructing new missiles at a factory that produced Pyongyang's first intercontinental ballistic missiles (ICBM) capable of reaching the US.
Newly obtained evidence, including satellite photos taken between July 20 and July 22, indicates that work is underway on at least one and possibly two liquid-fuelled ICBMs at a large research facility in Sanumdong, on the outskirts of Pyongyang, informed officials told The Washington Post on Monday.
The Sanumdong factory has produced two of North Korea's ICBMs, including the powerful Hwasong-15, the first with a proven range that could allow it to strike the US East Coast.
The evidence points to ongoing work on at least one Hwasong-15 at the Sanumdong plant, according to imagery collected by the National Geospatial-Intelligence Agency.
"We see them going to work, just as before," a US official told The Washington Post.
The exception, the officials said, is the Sohae Satellite Launching Station on North Korea's west coast, where workers can be observed dismantling an engine test stand.
The findings are the latest to show ongoing activity inside North Korea's nuclear and missile facilities at a time when the country's leaders are engaged in arms talks with the US.
The new intelligence does not suggest an expansion of North Korea's capabilities but shows that work on advanced weapons is continuing after US President Donald Trump last month declared that Pyongyang was "no longer a nuclear threat".
Monday's development come after revelations about a suspected uranium-enrichment facility, called Kangson, that North Korea is operating in secret.
Secretary of State Mike Pompeo acknowledged during a Senate testimony last week that North Korean factories "continue to produce fissile material" used in making nuclear weapons.
He however, declined to say whether Pyongyang was building new missiles.
During the historic June 12 Singapore summit between Trump and North Korea's Kim Jong-un, the Pyongyang leader agreed to "work toward" the "denuclearization" of the Korean Peninsula.
But since then, North Korea has made few tangible moves signalling an intention to disarm.