North Korea has been operating an undeclared long-range missile base near its border with China, according to a new report from the Washington-based Center for Strategic and International Studies. The Sinpung-dong installation, about 27 kilometres from Chinese territory in North Pyongan Province, is believed to store between six and nine nuclear-capable intercontinental ballistic missiles and their mobile launchers, giving Pyongyang the ability to strike targets across East Asia and the continental United States. Satellite imagery reviewed by CSIS shows that construction of the mountain-valley complex began around 2004 and that the facility became largely operational a decade later. Covering roughly 22 square kilometres, the base includes command buildings, missile maintenance halls, underground facilities and screened access points. Analysts say the missiles housed there are likely Hwasong-15 or Hwasong-18 models, though other advanced variants cannot be ruled out. Sinpung-dong is one of an estimated 15-to-20 ballistic-missile and warhead sites North Korea has never disclosed in disarmament talks, underscoring gaps in previous negotiations. Its location close to Chinese territory could complicate any pre-emptive strike calculations by the United States or its allies. South Korea’s defence ministry said it is closely tracking the site, which the report highlights as further evidence of Kim Jong Un’s push for a “rapid expansion” of his nuclear arsenal despite United Nations sanctions.