The U.S. announced in July it would set up Patriot Advanced Capability-3 missiles at Kadena Air Base and Kadena Ammunition Storage Area, both on Okinawa, following a series of missile tests by North Korea.
U.S. forces plan to set up four launch pads at Kadena, each fitted with six Patriot missiles, Kyodo News agency reported Monday, citing unnamed officials. Okinawa is about 1,000 miles southwest of Tokyo.
Earlier media reports said equipment for the launch pads arrived in Japan last week. The Patriot missiles were expected to arrive in the next two weeks, with the system set to start operating by the end of the year.
A Foreign Ministry official who refused to give his name said he had not heard of the American plans. Calls to the public affairs office of U.S. Forces Japan went unanswered late Monday.
The forthcoming PAC-3 deployment is the latest in a series of steps taken by the U.S. and Japan to beef up regional missile defense in response to North Korea's missile tests in July.
The seven missiles tested by the North included a long-range Taepodong-2, believed capable of hitting parts of the U.S., and drew international condemnation.
The U.S. announced its Patriot deployment plans later that month and said it would send 600 additional troops to Okinawa.
Earlier this week, the U.S. military also activated a high-powered "X-Band" radar outpost in northern Japan that is a key part of a joint missile defense shield and meant to track ballistic missiles in the region.
Washington has about 50,000 troops stationed in Japan under a mutual security pact.