They confirm what has become increasingly obvious in the past few months - that Mr Trump's summit with Mr Kim last June has done little to stop the North from consolidating its long-range nuclear capability.
According to CNN, satellite footage shows the Yeongjeo-dong base is still active, and another base seven miles away is being upgraded.
"Moreover, in the past year North Korea has significantly expanded a nearby facility that appears to be another missile base", said researchers at the Middlebury Institute of International Studies at Monterey.
The images, obtained by CNN, indicate North Korea began building a large, underground facility in 2017 and that construction was still ongoing as of August of this year.
North Korean efforts to upgrade and expand a long-range missile base come as no surprise to USA intelligence officials, who have always been wary of promises by Pyongyang to denuclearize. Trump's National Security Advisor John Bolton said the North has not lived up to those commitments yet.More news: SpaceX rocket sends worms, liquid fuel to Int'l Space Station
Experts told the USA 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.
North Korean Foreign Minister Ri Yong-ho arrived in China on Thursday on a three-day trip to secure Beijing's support for an easing of sanctions amid the continuing stalemate of denuclearisation talks with the US.
However, Ri's visit follows hard on the heels of last week's US-China summit in Argentina, which included discussion of North Korea.
-North Korea negotiations to dismantle Pyongyang's nuclear weapons program.
North Korea's leader Kim Jong Un with President Donald Trump at the U.S.More news: Huawei CFO wanted by the United States for conspiring to defraud banks
Some analysts say the activity is geared toward the continual development of nuclear-capable intercontinental ballistic missiles that could reach the USA mainland. "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.
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.
"Those missiles are being deployed at bases throughout North Korea, many of which have always been known to outside analysts", the report stated.
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. After a series of dubious talks, Trump claimed that he and Kim "fell in love" and that denuclearization of the Korean Peninsula would come "very, very quickly".
The base itself is strung along a narrow valley.More news: Thousands march in Brussels climate change demonstration