TOKYO — Defense Secretary Pete Hegseth called Japan on Sunday an “indispensable partner” in deterring growing Chinese assertiveness in the region and announced upgrading the U.S. military command in Japan to a new “war-fighting headquarters.”

Hegseth, who is on his first Asia trip with Japan as his second stop, also stressed the need for both countries to do more to accelerate the strengthening of their military capability as the region faces China’s assertive military actions and a possible Taiwan emergency.

“Japan is our indispensable partner in deterring Communist Chinese military aggression,” Hegseth said at the beginning of his talks with Japanese Defense Minister Gen Nakatani in Tokyo. “The U.S. is moving fast, as you know, to reestablish deterrence in this region and around the world.”

His comments come as an assurance at a time when Japan has been worried about how U.S. engagement in the region may change under President Donald Trump’s “America First” policy, Japanese defense officials said, speaking on condition of anonymity, citing protocol. Trump has also threatened to impose trade tariffs on Japan, a key U.S. ally, raising more concern.

The two sides agreed to accelerate plans to jointly develop and produce missiles such as Advanced Medium-Range Air to Air Missiles, or MRAAM, and consider producing SM-6 surface-to-air missiles, to help ease a shortage of munitions, Nakatani said. The ministers also agreed to speed up the process involving the maintenance of U.S. warships and warplanes in Japan to strengthen and complement Japanese and U.S. defense industries.

Japan and the U.S. decided in July to upgrade the command and control of the Japanese military as well as U.S. forces in the East Asian country, under the Biden administration, a major structural change aimed at bolstering joint operational and response capabilities. Japan is home to more than 50,000 U.S. troops.

Last week Tokyo launched the Japan Joint Operations Command, or JJOC, whose mission is to coordinate Japanese Ground, Maritime and Air Self-Defense Forces, in a significant action to further strengthen capabilities to respond to contingencies and better cooperate with the U.S.

Hegseth announced Sunday the upgrading of its current command, U.S. Forces Japan, by placing a unified operational commander to function as a joint force headquarters to liaise with its Japanese counterpart to serve as “war-fighting headquarters” to bolster speed and capability of their troops’ joint operations.

The Pentagon chief said the reorganization of U.S. troops is a step to better prepare for a possible conflict. America and Japan both work for peace, but “we must be prepared,” he said.

The Japanese defense officials say they are not expecting a significant change in their responsibilities or an increase in U.S. troops in Japan.

Hegseth and Nakatani told a joint news conference that they have also agreed on the need to beef up Japan’s defense posture on the Southwestern islands, which are in critical locations along disputed areas in the East China Sea and near Taiwan to further step up deterrence against China.

He stressed the need to have “sustaining, robust, ready and credible deterrence” in the Indo-Pacific, including across the Taiwan Strait, as “Japan would be on the frontlines of any contingency we might face in the western Pacific.”

China claims Taiwan as its own territory. The U.S. is obligated under a 1979 law to provide Taiwan with sufficient military hardware and technology to deter invasion, and its arm sales to Taiwan have always drawn strong opposition from Beijing.

On Saturday, Hegseth joined the U.S.-Japan joint memorial to honor the war dead in the Battle of Iwo Jima as they marked the 80th anniversary of the end of one of the fiercest battles of World War II, praising the strong alliance between the former enemies.

Before landing in Japan, Hegseth stopped in the Philippines where he also ensured Trump’s commitment to step up ties with the Southeast Asian country that faces maritime disputes with Beijing.