A total of 13 out of an estimated 20 active sites have been identified by the Beyond Parallel programme at the Centre for Strategic and International Studies (CSIS).
Satellite imagery reveals North Korean leader Kim Jong Un may not have been entirely truthful when he invited foreign journalists to witness the apparent demolition of its Punggye-ri nuclear test site.
In May, Sky News’ Asia correspondent Tom Cheshire was the only British broadcaster to watch a series of explosions at the facility ahead of talks between US President Donald Trump and Mr Kim.
But imagery of one of the sites identified by CSIS, located 84 miles (135km) northwest of Seoul, shows entrances to seven underground missile facilities and missile launchers hidden by camouflaged tarpaulin.
Construction began on the Sakkanmol Missile Operating Base between 1991 and 1993 and it is thought to have been completed in 2001, and added to since 2011 when Mr Kim came to power.
The CSIS report said the satellite imagery shows recent minor infrastructure changes, and as of November 2018 “the base is active and being reasonably well-maintained by North Korean standards”.
Pictured in the images are barracks, a parade ground, tunnel entrances, greenhouses, headquarters, support buildings, a cultural hall, vehicle storage and agricultural support buildings.
Experts at CSIS said: “The size of the entrances – as well as known Korean People’s Army (KPA) practices and the volume of soil removed – indicates that these tunnels could easily house all of the units transporter-erector launchers or mobile-erector launchers reload vehicles, other technical vehicles, and supplies.”
They said the entrances are often hidden from satellite imagery sight during spring and summer due to their location in a narrow tree-lined valley.
The Beyond Parallel programme is led by Victor Cha, who was a candidate to become Washington’s ambassador to South Korea, a position which has yet to be filled by Mr Trump.
Its report could prove a sticking point for the US, whose president and Secretary of State Mike Pompeo are trying to hold Mr Kim to denuclearisation promises he has made since the US-North Korea summit in Singapore in June.
“We have known for some time that the North Koreans are starting to deploy and even test missiles at the unit level,” Stephan Haggard, a professor of Korea-Pacific studies at the University of California at San Diego said.
“The last round of tests under Kim Jong Un were not just coming from missile test sites. What [the CSIS reports show] is how hard it will be to really cap the programme.
“And of course, no one seriously believes that North Korea’s underlying capability has been neutralised. That is a fantasy.
“The only thing we have at the moment is a freeze on testing, which could, of course, be reversed easily.”
In a separate report released this week, CSIS said: “After extensive research, including interviews with North Korean defectors and government, defence and intelligence officials around the world, many of these issues have been addressed and it appears that the KPA currently has approximately 15-20 missile operating bases.”