WASHINGTON (Reuters) - One of 20 undeclared ballistic missile operating bases in North Korea serves as a missile headquarters, according to a report by the Center for Strategic and International Studies (CSIS) published on Monday.

FILE PHOTO: Intercontinental ballistic missiles are seen at a grand military parade celebrating the 70th founding anniversary of the Korean People's Army at the Kim Il Sung Square in Pyongyang, in this photo released by North Korea's Korean Central News Agency (KCNA) February 9, 2018. KCNA/via REUTERS

“The Sino-ri missile operating base and the Nodong missiles deployed at this location fit into North Korea’s presumed nuclear military strategy by providing an operational-level nuclear or conventional first strike capability,” said the report co-authored by analyst Victor Cha.

The discovery of an undeclared missile headquarters comes three days after U.S. President Donald Trump said he “looks forward” to another summit to discuss denuclearization with North Korean leader Kim Jong Un in late February.

Kim vowed to work toward denuclearization at his first summit with Trump in June, but there has since been little concrete progress.

The White House did not immediately respond to a request for comment.

CSIS, which last reported on the 20 missile bases in November, said the Sino-ri base has never been declared by North Korea and as a result “does not appear to be the subject of denuclearization negotiations.”

The report said that missile operating bases would presumably be subject to declaration, verification, and dismantlement in any nuclear deal.

“The North Koreans are not going to negotiate over things they don’t disclose,” said Cha.

“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 sites.

Located 132 miles (212 km) north of the demilitarized zone, the Sino-ri complex is a seven-square-mile (18-square-km) base that plays a key role in developing ballistic missiles capable of reaching South Korea, Japan, and even the U.S. territory of Guam in the Western Pacific, the report said.

It houses a regiment-sized unit equipped with Nodong-1 medium-range ballistic missiles, the report added.

Satellite images of the base from Dec. 27, 2018 show an entrance to an underground bunker, reinforced shelters and a headquarters, the report said.

In South Korea, the Sino-ri facility has long been known as one of the bases housing the Nodong, also called the Rodong, a medium-range missile based on Soviet-era Scud technology that the North began deploying in the mid-1990s.

“It is a facility we’ve been monitoring with interest, in cooperation with the United States,” Kim Joon-rak, a spokesman for South Korea’s Joint Chiefs of Staff, told a news briefing on Tuesday.