China's increased reliance on nonnaval ships to assert its claims in the South China Sea is complicating U.S. efforts to avoid a clash in the disputed waters, according to 7th Fleet commander Vice Adm. Joseph Aucoin.

While the U.S. and Chinese navies are working more closely under an agreed code for unplanned encounters at sea, the deployment of coast guard and other nonnaval vessels in the area is "a concern of mine," Aucoin told reporters Monday in Singapore. He plans to take the USS Blue Ridge, the command ship of the 7th Fleet, to China later in the summer.

"We have all types of senior level engagements with the Chinese PLAN, that we meet pretty routinely," Aucoin said, referring to the People's Liberation Army Navy. He said he had a "greater fear" about other actors, "whether it's coast guard or what we refer to as white shipping or cabbage ships, not sure about their professionalism."