The United States and Japan must expand their defense cooperation with like-minded nations to ensure the protection of a rules-based order in the Asia-Pacific region, the commander of the U.S. Pacific Command said in Tokyo on Wednesday.

Adm. Harry Harris spoke at a forum of current and retired U.S. and Japanese top brass in the wake of an international tribunal's ruling that China's claims to historic and economic rights over most of the South China Sea have no legal basis.

Harris said that while China is responsible for provocative activities that raise the level of tension in East Asia, it is still reasonable to hope that the country will be "a responsible actor."

"We can choose to treat China in a negative way, or we can choose to encourage China to join the rest of us in this multinational rules-based order," Harris said.

Harris said the strength of the Japan-U.S. alliance and the success of drills bringing the two countries together with South Korea and India indicate such multilateral action is the right way to handle the region's security issues.

He hailed China's participation in the Rim of the Pacific, or RIMPAC, exercise set to run through Aug. 4, which includes Japan, the United States and a host of other maritime nations.

During his four-day visit to Japan from Sunday, Harris met with several senior Japanese officials, including Defense Minister Gen Nakatani.