North Korea has clandestinely expanded one of its main long-range missile development bases during recent months, according to new reports based on satellite imagery collected during October and November.

The imagery, provided by the Middlebury Institute of International Studies at Monterey and first reported by CNN, show upgrades being made the Yeongjeo-dong missile base, as well as construction of a new facility nearby in North Korea’s mountainous interior.

Analysts say the Yeongjeo-dong base was previously well known to U.S. intelligence, but that the new facility nearby has never before been revealed.

There was no immediate reaction from the Trump administration Thursday to the reports that raised concern in national security circles about the pace of denuclearization talks between Washington and Pyongyang.

CNN and other media, including The New York Times and Britain’s Guardian newspaper, framed the development as undermining the administration’s pursuit of diplomacy with North Korean leader Kim Jong-un.

The missile base activity and construction shown by the satellite imagery over Yeongjeo-dong occurred after Mr. Kim agreed during a major summit with President Trump in Singapore in June to abandon North Korea’s nuclear weapons program.

Some analysts say the activity is geared toward the continual development of nuclear-capable intercontinental ballistic missiles that could reach the U.S. mainland.

The developments come against a backdrop in which Mr. Trump and his advisers say they are hoping for a second summit with Mr. Kim to discuss progress — or the lack thereof — toward denuclearization.

While the Kim regime has not carried out a long-range missile or nuclear weapons test since talks with South Korea and the U.S. gained momentum early this year, satellite imagery like that circulating Wednesday and Thursday has emerged on multiple occasions in recent months, showing continued missile base activity in North Korea.

The latest imagery became public just as North Korea’s foreign minister arrived in China for talks with Chinese officials.

China is North Korea’s most important economic partner and political ally, but has agreed to work with Washington to implement United Nations economic sanctions aimed at pressuring Mr. Kim to abandon his nuclear weapons program.

North Korea has developed the program over recent decades in continual violation of repeated U.N. Security Council resolutions.

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