WASHINGTON — With a second U.S.-North Korea nuclear summit looming in February, researchers have discovered a secret ballistic missile base in North Korea — one of as many as 20 undisclosed missile sites in the country, according to the researchers’ new report.

The Kim regime has never disclosed the existence of the Sino-ri Missile Operating Base to the outside world. Ballistic missiles are the primary delivery mechanism for North Korean nuclear warheads.

The report from Beyond Parallel, a project sponsored by the Center for Strategic and International Studies (CSIS), a defense think tank, was released Monday and comes after an announcement Friday that President Donald Trump "looks forward" to meeting with Chairman Kim Jong Un next month "at a place to be announced at a later date."

The White House declined to comment on the report.

"The North Koreans are not going to negotiate over things they don’t disclose," said Victor Cha, one of the authors of the report. "It looks like they’re playing a game. They’re still going to have all this operational capability," even if they destroy their disclosed nuclear facilities.

Cha says the base is "clearly a mainstay of their strategic missile force," but there are no indications it is part of any discussions on denuclearization.

Situated about 130 miles north of the DMZ, Sino-ri Missile Operating Base houses the headquarters for the Korean People’s Army Strategic Rocket Forces missile brigade, a unit responsible for ballistic missiles. The base has been central to developing ballistic missiles that are capable of reaching South Korea, Japan, and even Guam, according to the report.

Click here to read the report

Beyond Parallel researchers estimate North Korea has 20 undisclosed sites where it continues to develop its ballistic missile program. Sino-ri is one of the oldest of those sites but is still operational today. Satellite photos dated Dec. 27, 2018, show an entrance to an underground bunker, hardened shelters, and a headquarters area, according to Beyond Parallel. The underground bunkers have rock and dirt berms in front that appear to protect them from artillery fire and airstrikes. The base is just under 7 square miles in size.

Sino-ri is supported by two nearby facilities, the Sobaek-su Academy and Myodu-san training area.

The Sobaek-su Academy was established in the late 1950s or 1960s as an artillery officer’s school and expanded in the following decades, becoming a ballistic missile school early this century, according to the report.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The school not only educates Strategic Rocket Forces officers, but it may also conduct research on "ballistic missile design and operation," the report says. Satellite photos show buildings suspected to hold barracks and classrooms, vehicle storage facilities, and an entrance to an underground facility.

The Myodu-san training area sits less than a mile from the academy and may serve as the training facility for the both the Sino-ri missile base and the academy.

Overview of the Sino-ri Missile Operating Base, Sobaek-su Academy, and Myodu-san training area on Dec. 28, 2018. European Space Agency / Beyond Parallel

Cha, a former National Security Council official focused on Asian affairs, agreed that the trip to Beijing was a sign Kim is readying for the next meeting.

"This happened last time, too. Kim Jong Un has more leverage in the meeting if he’s just met with Chinese," Cha said, adding, "The Chinese want to make sure that they see Kim before he has another meeting with the U.S. too."

The Trump administration tapped Cha as ambassador to South Korea, but his nomination was withdrawn in early 2018 because of policy disagreements.

On Sunday, Trump tweeted about a possible second summit, saying he is "looking forward to meeting with Chairman Kim at the end of February!" Trump also wrote, "The Media is not giving us credit for the tremendous progress we have made with North Korea."

The Media is not giving us credit for the tremendous progress we have made with North Korea. Think of where we were at the end of the Obama Administration compared to now. Great meeting this week with top Reps. Looking forward to meeting with Chairman Kim at end of February! — Donald J. Trump (@realDonaldTrump) January 20, 2019

But a former senior U.S. official briefed on the current negotiations says administration officials and America's allies in the region are nervous that Trump will give up a lot without getting much, if anything, during the upcoming summit with Kim. Those concerns have escalated since Trump's Syria announcement on troop withdrawal after speaking with President Recep Tayyip Erdogan of Turkey. Japanese officials in particular are "extremely nervous."

"They’re incredibly uncomfortable," the former official said.

They anticipate Trump could agree to international sanctions relief, a liaison office in Pyongyang and an end-of-war declaration, the official said, adding that North Korean officials have told Secretary of State Mike Pompeo they want sanctions relief but the end-of-war declaration is not as much of a priority.

Many good conversations with North Korea-it is going well! In the meantime, no Rocket Launches or Nuclear Testing in 8 months. All of Asia is thrilled. Only the Opposition Party, which includes the Fake News, is complaining. If not for me, we would now be at War with North Korea! — Donald J. Trump (@realDonaldTrump) July 3, 2018

Some Trump administration officials and U.S. allies are nervous because there is still so little known about what Kim and Trump talked about when they met in Singapore last year. Only the interpreter knows, the official said.

"I don’t think the president is telling anyone what he told him," the former official said, so the North Koreans can use that to tell American negotiators whatever they want about what Trump said.

Trump said in July via Twitter that the recent lack of North Korean missile launches is a sign that his approach is working.

The Syria announcement has solidified for world leaders, including those in Japan and South Korea, that the only thing that matters in terms of achieving the U.S. position they want is getting a one-on-one with Trump. "They all know that you’ve got to get to the president and that the president, because he doesn’t study that much, is probably an easy mark," the former official said. "This is a leader game. They’re all trying to get to him. That’s why there’s so much anxiety."

The Sino-ri headquarters area on April 4, 2018. Beyond Parallel / Digital Globe

There is also concern that Trump will fall back on his threats to withdraw troops from the Korean Peninsula. The recent failure to complete the Special Measures Agreement, a regularly renewed five-year defense pact between the U.S. and South Korea, increases the chances of a fight in the alliance, and that precipitates withdrawal, the former official said.

"I can’t find anybody in the U.S. who thinks the North Koreans are denuclearizing," the former official said. "There was a reluctant conclusion that they had to roll the dice on another summit" to get negotiations moving again.

Jung Pak, a former U.S. intelligence officer who has long tracked North Korea and is now a senior fellow at the Brookings Institution, said experts both inside and outside the government don’t believe Kim is ready to give up his nuclear arsenal.

Paul Cheung / NBC News

"Credible Korea experts and watchers assess that Kim is highly unlikely to give up its nuclear weapons," Pak told NBC News.

The U.S. government assesses that North Korean ballistic missile development and activity has continued throughout 2018 and into 2019, but North Korea’s actions have not been as aggressive as in 2017 when it launched about two-dozen missiles during 16 tests. North Korea’s missile program made dramatic strides in 2017 with numerous ICBM launches and while the launches ceased in 2018, the development did not.

Despite the U.S. desire for the North Koreans to provide a full accounting of their ballistic missile sites and nuclear weapons program, North Korea has not yet done so.

The Trump administration says the discussions with the North have already produced progress by lowering tensions, and that the regime has not conducted new missile or nuclear tests since the diplomacy began.

But former officials and lawmakers say North Korea remains an unpredictable danger to the U.S. and its allies, with an increasingly capable nuclear and missile arsenal.

"Tensions have been reduced. But the North Korean threat has not been reduced," Pak said. "Those are two different things."

U.S. officials also acknowledge that North Korea continues to produce fissile material for weapons.