Rear Adm. Rick Wren, the commander of the Japan-based aircraft carrier USS Kitty Hawk's battle group, told The Associated Press that Washington wants China to become a stabilizing force in Asia, but that it has some reservations about Beijing's military expansion.

"Certainly we are a bit wary of China," Wren told the AP aboard the carrier during a port visit to Sydney, Australia. "They seem to be fairly opaque in communicating what they intend to do with this large military buildup."

"We need the Chinese to be a strong and stable partner in the global economy, as they already are," he said.

"Certainly we need them to be a stabilizing force in this region. But until we can actually define that, we will continue to practice our skills and be ready for whatever the president calls on us to do."

Wren, whose ships have just finished major joint military exercises with Australia, said multi-country alliances in the Asia-Pacific were "very important" to the United States.

Japan took part in the Talisman Saber exercises as an observer, and Wren said Japan would take a "much bigger" role in future exercises. He did not elaborate.

"The importance of multilateral alliance in this theater is very important," Wren said, referring to the Asia-Pacific. "What we both want to do is expand that in the interest of creating a stronger and long-lasting regional stability, and so we are bringing in many, many other nations."

He said relationships were not limited to cooperation in combat roles, but included things such as humanitarian missions and providing natural disaster relief.

The biennial Talisman Saber exercise pits 20,000 U.S. troops and 7,500 Australian forces against fictional enemies in a variety of land and sea-based scenarios designed to test their skills in combat, peacekeeping and humanitarian relief efforts.

The two-week exercise included 10 U.S. ships, 20 Australian ships and 125 aircraft operating off Australia's northeastern coast.

The exercise was held as the United States and Japan step up efforts to build a joint missile defense system in Asia, partly as a bulwark against regional threats such as a nuclear-armed North Korea.

Australia, a steadfast U.S. ally that maintains around 2,000 troops in Afghanistan and Iraq, is studying whether to participate in the defense shield.

Australia and Japan signed a security agreement in March that will enable Japanese forces to train alongside Australians for disaster relief and peacekeeping missions, and boost cooperation between the two countries in counterterrorism measures and intelligence sharing.