The missile base activity and construction shown by the satellite imagery over Yeongjeo-dong occurred after Mr. Kim agreed during a major summit with President Trump in Singapore in June to abandon North Korea's nuclear weapons program.
According to CNN, the imagery offers evidence the Yeongjeo-dong missile base and a nearby, previously unreported site remain active and have been continuously upgraded.
"Satellite images show that the base remains active".
Lewis and Schmerler said they were still not sure whether Yeongjeo-dong and the new facility under construction in nearby Hoejung-ni, both in the mountainous area near North Korea's central border with China, were separate bases or parts of a larger single operation.
But National Security Adviser John Bolton said Tuesday that there should be another summit with Kim.
South Korean Foreign Minister Kang Kyung-wha and US Secretary of State Mike Pompeo will hold talks in Washington on Thursday to discuss North Korea's denuclearization among other issues, it was announced here.
In a statement the Pentagon said: "We watch North Korea very closely but we can not discuss intelligence". We continue to support the diplomatic process.
However, Ri's visit follows hard on the heels of last week's US-China summit in Argentina, which included discussion of North Korea.More news: Diamondbacks Trade All-Star First Baseman Paul Goldschmidt to Cardinals
Since the Singapore meeting, talks between North Korea and the United States have stalled over how to eradicate the North's nuclear weapons program.
The revelation is yet another blow to President Donald Trump, who after first trying to face down North Korean dictator Kim Jong Un and belittle him as a "Little Rocket Man" who would be met with "fire and fury", then sought to prove his dealmaking prowess by getting Kim to agree to denuclearization.
Some analysts say the activity is geared toward the continual development of nuclear-capable intercontinental ballistic missiles that could reach the USA mainland.
Bolton said the USA would press ahead with a second meeting shortly after the start of the new year - saying, "January, February" - in the hope of making further progress. "Any denuclearization agreement would require North Korea to allow worldwide inspectors to determine that these units are no longer armed with nuclear weapons", according to the report from Lewis and Schmerler.
The North officially suspended its nuclear and missile tests ahead of the June summit, and missile production and deployment does not technically violate any agreement between Pyongyang and the US and South Korea.
One such facility is the missile base near Yeongjeo-dong, a site that has long concerned US and South Korean officials and the subject of the analysis of the new images released Wednesday.
That missile was considered by some experts to be capable of reaching any part of the continental United States, although North Korea is not yet believed to have the ability to deliver nuclear warheads on such missiles.