A U.S. Navy admiral expressed new concern Friday over China's military buildup and urged Beijing to be clearer about its intentions.

With China's military growing at an "unprecedented rate," the U.S. wants to ensure that expansion doesn't destabilize the region, Rear Adm. Kevin Donegan told reporters on a visit to the Chinese territory of Hong Kong.

Donegan referred to China's expanded weaponry. His remarks echoed the concerns of other U.S. military leaders who have said the growth in China's military spending — up almost 15 percent in the 2009 budget — raises questions about how Beijing plans on deploying its new power.

"When we see a military growing at that rate, we're interested in transparency and the understanding of the uses of that military," said Donegan, commander of the USS George Washington aircraft carrier strike group, a key part of the U.S. Pacific Fleet.

Donegan's comments come as a top Chinese general visits the United States on a mission to strengthen trust between the two militaries and dispel U.S. concerns about the growth of the People's Liberation Army.

Xu Caihou, the PLA's second-highest ranking officer, told President Barack Obama on Wednesday that ties between the two countries' militaries play "an important role in enhancing strategic mutual trust and deepening their pragmatic cooperation," according to Chinese media reports.

China has boosted military spending by more than 10 percent annually for almost two decades, and the official figure of $71 billion this year is thought by many analysts to represent only a portion of total defense spending. It still amounts to only a fraction of U.S. defense spending.

China says much of the increase is used to improve salaries and living conditions for soldiers, but it has also been adding sophisticated new warships, submarines, fighter jets and other weapons systems to its arsenal. PLA leaders have also said they are considering building an aircraft carrier, but such a development is thought to be years, if not decades, away.

Donegan acknowledged the possibility of a Chinese aircraft carrier, but also said he was concerned with anti-access weapons. This class of weapons includes missiles and submarines that can threaten U.S. forces in the region and prevent them responding in the event of a crisis.

"I am absolutely concerned," Donegan said.

He went on to say, "When a navy is doing that, we just want to make sure it's transparent enough so those in the region understand what they're doing."

At the same time, Donegan described positive exchanges between the two militaries that he said he hoped would continue, including a visit by five Chinese army generals aboard the George Washington during its call in Hong Kong this week.

Ties between the two militaries have been repeatedly roiled by China's objections to U.S. arms sales to Taiwan, claimed by Beijing as its own territory, as well as Chinese efforts to disrupt Navy surveillance missions off its shores.

A series of confrontations involving vessels from the two navies has raised concerns over China's rising determination to defend what it sees as its territorial interests in the South China Sea, where the U.S. has long operated as the major international power.

Donegan said the Navy would continue to operate in international waters — something that could come in defiance of Beijing's claims it has the right to bar surveillance work inside its exclusive economic zone.

"We are going to continue to operate in the South China Sea and international waters and not in territorial seas of another country," he said.