U.S. Defense Secretary Robert Gates said the U.S. has a stake in the growing number of disputes about ownership of Asian island chains and ship routes through waters China claims.

"We have a national interest in freedom of navigation, in unimpeded economic development and commerce and in respect for international law," Gates told a regional security forum of defense ministers in the Vietnamese capital.

The message was strong and the audience unmistakable, but Gates avoided a direct confrontation with China. He never mentioned the country by name during a brief address to the group of security ministers, which included a top Chinese general.

Several Asian countries have expressed concern over increasingly aggressive maritime moves by the Communist giant, including its response to a ship collision last month off disputed islands in the East China Sea that plunged relations between China and Japan to a five-year low. Relations have since improved, but both countries continue to claim sovereignty over the territory, known as Senkaku in Japan and Diaoyu in China.

China tried to ease tensions Tuesday by reassuring its neighbors that it wants to work together.

"China pursues a defense policy that is defensive in nature. China's defense development is not aimed to challenge or threaten anyone, but to ensure its security and promote international and regional peace and stability," Chinese Gen. Liang Guanglie said in a speech to his counterparts. "Security of a country relies not only on self-defense capabilities, but also on mutual trust with others."

Defense ministers from the 10-member Association of Southeast Asian Nations, along with their counterparts from the United States, China, Russia, Japan, Australia, New Zealand, India and South Korea attended the meeting Tuesday in Vietnam's capital.

China considers the U.S. position on maritime navigation and security to be outside meddling in Asian affairs. Beijing was irate when U.S. Secretary of State Hillary Rodham Clinton used similar language in July.

"The United States has always exercised our rights and supported the rights of others to transit through, and operate in, international waters," Gates said. "This will not change, nor will our commitment to engage in activities and exercises together with our allies and partners."

Gates was referring, in part, to China's claim to control water far off its coastline that the United States considers open water under international law. He also was reaffirming U.S. support for Southeast Asian nations that feel threatened by China and want U.S. backing even as they try to maintain cordial relations with their much larger Asian neighbor.

Among the disputed island chains are the Spratly and Paracel island chains in the South China Sea - claimed by China and several of its Southeast Asian neighbors, including Vietnam - and the East China Sea islands that both Tokyo and Beijing claim.

The United States is worried that territorial disputes over islands in the South China Sea could imperil strategic international shipping lanes, and analysts have warned that China's newly aggressive moves to claim the areas could ignite a shooting war.

Gates' goal in Vietnam was twofold: to make the point about the limits of Chinese control and to patch up damaged U.S. military ties with that country.

The event "takes place in the backdrop of a regional and international situation which has seen rapid and complicated developments," Vietnamese Prime Minister Nguyen Tan Dung said. "We are often faced with grave security challenges, both traditional and nontraditional."

A day earlier, Liang met with Gates, ending a freeze on military contacts meant to protest a $6.4 billion U.S. arms package for Taiwan, the self-governing island that China claims as its own territory.

After the meeting, Gates said he accepted a formal invitation to visit Beijing, which will likely occur early next year.

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Associated Press writers Tran Van Minh and Margie Mason contributed to this report.