The new X-band radar system is designed to protect the region against the North Korean threat, boosting Japan's ability to track and intercept missiles from across the Sea of Japan. Officials have stressed it is not directed at China. Kerry acknowledged the threat from Pyongyang, but he also said the U.S. was willing to sign a non-aggression pact with North Korea if it gives up its nuclear weapons and complies with international demands.
The drones, meanwhile, are intended to help step up surveillance around the Senkaku islands, a source of heated debate between Japan and China. While the U.S. has operated unmanned aircraft over Japan in the past, for example during the 2011 tsunami, this would be the first time that drones would be based on a U.S. base in Japan.
Hagel said the U.S. reiterated that while Washington takes no side on the question of the islands' sovereignty, it recognizes Japan's administration of them and has responsibilities to protect Japanese territory under a mutual defense treaty.
"We strongly oppose any unilateral or coercive action that seeks to undermine Japan's administrative control," he said.
China's Foreign Ministry did not immediately respond to a request for comment Thursday, which fell during a weeklong national holiday. Beijing has criticized the installation of the first military radar system, announced last month, to monitor Pyongyang's military activities. Foreign ministry spokesman Hong Lei then said the plans could affect regional stability and upset the strategic balance.
The U.S. has watched warily as the Senkakus issue has badly soured China-Japan relations and led to bellicose talk and actions from both sides. China has increased patrols near the islands that it calls Diaoyu.
Successive U.S. administrations have maintained that the two nations must sort out their differences over the Senkakus peacefully. U.S. officials said the position was so well-known that there was no need to address it directly in the documents agreed upon Thursday.
Japanese Foreign Minister Fumio Kishida said the overall security environment "has become increasingly severe." He added, "We are decidedly opposed to the attempt to change the status quo through coercion. Rule of law is critically important."
Kerry said the U.S. continues to have frank discussions with China, laying out "lines that shouldn't be crossed." He added that "a rising China is welcome as long as that China wants to engage according to international standards."
The islands, also claimed by Taiwan, stir a depth of nationalist passion that belies their size and remoteness. They are located roughly midway between Taiwan and the southern Japanese island of Okinawa and cover a total area of just 2.3 square miles.
A senior U.S. official said the new radar, which was initially announced by then-Defense Secretary Leon Panetta about a year ago, will provide better coverage in the event of a North Korean attack. One of the X-band radar systems is already positioned in northern Japan, but the official said the second one, to be located in the Kyoto Prefecture, will fill gaps in coverage.
The official said details about the deployment of the U.S. Global Hawk drones were still being worked out. The plans also included deployment of F-35 jet fighters for the Marines around 2017. And for the first time, the U.S. will deploy Navy P-8 anti-submarine aircraft outside the U.S., sending them to Japan later this year.
More broadly, the 10-page statement signed by Kerry and Hagel was designed to improve military and diplomatic relations with Japan while working to reduce America's troop footprint on the island.
The U.S. force of 50,000, particularly troops in Okinawa, has increased tensions between the two nations over the military's land use, crimes committed by service members and disruptions by military flights in the heavily populated region. Under plans announced last year, about 9,000 Marines stationed on Okinawa will be moved out, with 5,000 going to Guam.
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Associated Press writer Didi Tang in Beijing contributed to this report.