North Korean leader Kim Jong Un
North Korean leader Kim Jong UnReuters

New satellite images obtained by CNN reveal that North Korea has significantly expanded a key long-range missile base located in the mountainous interior of the country.

The satellite imagery, presented by the network on Wednesday, offers evidence that the Yeongjeo-dong missile base and a nearby, previously unreported site remain active and have been continuously upgraded.

While the base at Yeongjeo-dong has long been known to US intelligence agencies and analysts, researchers at the Middlebury Institute of International Studies at Monterey told CNN that the images reveal construction on a new facility just seven miles away from the older site that had not been previously publicly identified.

"Satellite images show that the base remains active. Moreover, in the past year North Korea has significantly expanded a nearby facility that appears to be another missile base," the report states, noting that it is unclear whether the two bases are separate, or whether one is subordinate to other.

The images indicate that North Korea was building an extremely large underground facility in 2017 and that this facility was still under construction as of August 2018, according to CNN.

"Construction on the previously unidentified site has continued even after the Singapore Summit" between Kim and President Donald Trump in June, Jeffrey Lewis of the Middlebury Institute of International Studies at Monterey, one of the analysts that identified the site, told CNN. "Whatever Kim says about his desire for denuclearization, North Korea continues to produce and deploy nuclear armed missiles."

The site's unique location makes it a strong candidate to receive North Korea's newest long-range missiles, including those that can carry nuclear weapons and can strike the United States, according to Lewis and his colleague David Schmerler.

US officials have long said they are not surprised by similar open source findings, but have declined to offer any additional response when other sites have been identified.

The report comes as contacts continue between the US and North Korea on denuclearization.

Kim and Trump held a historic summit in Singapore last June, during which they signed an agreement which includes a commitment to achieve total denuclearization of Korea, with promises to pursue “vigorous negotiations” to that end.

Subsequent reports suggested, however, that despite its commitment to denuclearize, North Korea has continued to expand infrastructure at nuclear and missile sites.

Last month it was reported that Kim had inspected the site for testing a “newly developed cutting-edge strategic weapon”.

A subsequent report, however, suggested that Kim is willing to allow inspectors into the country's main nuclear complex in Yongbyon.

Last week, Trump said he hoped to organize a follow-up meeting with Kim for early 2019.

"We're getting along very well. We have a good relationship," he said. Asked if he would ever host the North Korean leader in the United States, Trump replied, "At some point, yeah."

Responding to the satellite images, Pentagon spokesperson Lt. Col. Chris Logan told CNN, "We watch North Korea very closely. We continue to support the diplomatic process. We will not discuss matters of intelligence."

The State Department declined to comment, saying it does not discuss intelligence matters.