SEOUL, South Korea (AFP) — North Korea has built a secret military base near its border with China which may house Pyongyang’s newest long-range ballistic missiles, according to new research.

The “undeclared” Sinpung-dong Missile Operating Base lies about 27 kilometers from the Chinese frontier, the Washington-based Center for Strategic and International Studies (CSIS) said in a report published Wednesday.

The facility in North Pyongan Province likely houses six to nine nuclear-capable intercontinental ballistic missiles (ICBMs) and their launchers, the study said.

It said the weapons “pose a potential nuclear threat to East Asia and the continental United States.”

North Korea has ramped up its nuclear weapons program since a failed summit with the US in 2019, and leader Kim Jong Un recently called for the “rapid expansion” of the diplomatically isolated nation’s nuclear capability.

The report — which CSIS called the first in-depth, open-source confirmation of Sinpung-dong — said the base is one of about “15-20 ballistic missile bases, maintenance, support, missile storage, and warhead storage facilities which North Korea has never declared.”

The facility is “not known to have been the subject of any denuclearization negotiations previously conducted between the United States and North Korea,” the study said.

Citing their analysts’ current assessments, CSIS said the launchers and missiles could leave the base in times of crisis or war, link up with special units and conduct harder-to-detect launches from other parts of the country.

The base, along with others, “represent the primary components of what is presumed to be North Korea’s evolving ballistic missile strategy, and its expanding strategic-level nuclear deterrence and strike capabilities,” the report said.

Kim’s 2019 summit with US President Donald Trump in Hanoi, Vietnam, collapsed because the two sides disagreed on what Pyongyang would concede in return for sanctions relief.

Since then, North Korea has repeatedly said it will never give up its weapons and declared itself an “irreversible” nuclear state.

And in the wake of Russia’s invasion of Ukraine, Pyongyang has drawn closer to Moscow.

South Korean and Western intelligence agencies have said the North sent over 10,000 soldiers to Russia in 2024 — primarily to the Kursk region — along with artillery shells, missiles and long-range rocket systems.

Trump has held high-profile talks with Russian and Ukrainian leaders in recent days in a bid to end the conflict.

Washington has said there is evidence that Russia is stepping up support for North Korea, including providing help on advanced space and satellite technology, in return for its assistance in fighting Ukraine.

Analysts say satellite launchers and ICBMs share much of the same underlying technology.