North Korea has a clandestine base that houses intermediate-range ballistic missiles capable of hitting Okinawa Prefecture, a U.S. think tank said Friday.

The Sangnam-ni missile operating base, located 250 km north of the demilitarized zone dividing the two Koreas, is one of an estimated 20 undeclared ballistic missile bases in North Korea, the Center for Strategic and International Studies said in a report.

The report came ahead of a second summit between U.S. President Donald Trump and North Korean leader Kim Jong Un slated for Feb. 27 and 28 in Hanoi.

The deployment of the Hwasong-10, with a range of more than 3,000 km, at Sangnam-ni is "a component of North Korea's presumed offensive ballistic missile strategy that provides a strategic-level first strike capability against targets located throughout East Asia as far as U.S. forces in Okinawa and Guam," it said.

However, the base does not appear to be the subject of denuclearization negotiations between Washington and Pyongyang, according to the report.

The CSIS warned any potential summit agreement that would lead to the dismantling of only the key missile test site in Tongchang-ri, to which North Korea has already committed, "would obscure the extant military threat to U.S. forces and South Korea from this and other undeclared ballistic missile bases."