Washington and Tokyo agreed on Monday to install a second radar-based defense system in Japan aimed at countering the potential missile threat from North Korea, the New York Times reported.
The agreement came during a visit to Tokyo by U.S. Defense Secretary Leon Panetta, who is on a week-long Asian trip including visits to China and New Zealand.
"The purpose of this is to enhance our ability to defend Japan," Panetta told a news conference. "It's also designed to help forward-deployed U.S. forces, and it also will be effective in protecting the U.S. homeland from the North Korean ballistic missile threat."
The exact location of the advanced missile defense radar has not yet been decided.
The deal is likely to cause concern in Beijing, which is locked in a bitter territorial dispute with Tokyo, but Panetta said the radar system would not be directed at China.
Japan already hosts similar U.S. X-band radars, officially known as the AN/TPY-2.
International concern over North Korea's ballistic missiles has heightened after Pyongyang conducted a long-range rocket launch in April in defiance of a UN ban.
The launch failed and the rocket, which Pyonyang said was due to put a satellite into orbit, exploded shortly after takeoff and fell into the sea.