BEIJING—The top U.S. military officer began a visit to Beijing aimed at improving chilly military relations with an appeal Sunday for a peaceful settlement amid tensions in the disputed South China Sea.

The visit by Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, is the first of its kind in four years. The two governments are trying to improve military-to-military ties after setbacks over U.S. arms sales to Taiwan, cyberattacks traced to China and concern about Beijing’s military buildup.

Speaking to reporters ahead of meetings with Chinese officials, Mullen said that sound ties between what he called the two “Pacific powers” are vital.

“Frankly, I think we need to work a lot harder on strategic trust and transparency,” Mullen said.

The admiral referred repeatedly to Washington’s commitments to Asian allies and a prominent regional role. That indicated Beijing will face resistance to any pressure for a smaller U.S. presence as Chinese military power grows.

“The U.S. is not going away,” Mullen said. “Our enduring presence in this region has been important to our allies for decades, and it will continue to be so.”

A key area of dispute is the South China Sea, where Beijing and neighbors including the Philippines and Vietnam have conflicting claims. Beijing claims the whole sea as its waters and reacted angrily last month to a U.S. Senate resolution criticizing its use of force in incidents between Chinese vessels and those of other nations. Washington insists its navy has a right to cross the sea and to collect surveillance data.

“We seek to strongly support the peaceful resolution of these differences,” Mullen said. “The worry, among others, that I have is that the ongoing incidents could spark a miscalculation and an outbreak that no one anticipated.”

Beijing froze military relations last year after Washington announced an arms sale to Taiwan, the self-ruled island the communist mainland claims as part of its territory.

A thaw began when then-U.S. Defense Secretary Robert Gates visited Beijing in January, followed by a trip to Washington by Chinese President Hu Jintao.

In May, a Chinese delegation led by Mullen’s counterpart, Gen. Chen Bingde, visited Washington and U.S. military facilities in the first visit of its kind since 2004.

During his visit, Mullen was due to meet with Chen and other military officials, speak at a university in Beijing and visit Chinese bases.

Mullen said Washington welcomes China’s military development if it helps to solve global problems such as piracy. But he said Washington also wants to clarify Beijing’s intentions.

China’s military budget of $95 billion this year is the world’s second-highest after Washington’s planned $650 billion in defense spending. Beijing is developing weapons such as the “carrier killer” DF 21D missile that analysts say might threaten U.S. warships and alter the regional balance of power.

“There are some very specific capabilities that are being developed here that are very focused on the United States capability,” Mullen said.