"Absent clarification from China, its military modernisation efforts hold significant implications for regional stability," the US Pacific Command Commander Admiral Robert Willard, said in his testimony before House Armed Services Committee.
The region is developing its own conclusions about why the People's Liberation Army (PLA) continues to expand its ability to project power outside China's borders, and to range both US forces and its allies and partners in the region with new anti-access and area-denial weaponry.
Willard said China's rise will largely define Asia-Pacific environment in the 21st century.
He said China's naval activities are a direct challenge to accepted interpretations of international law and established international norms.
"Of growing concern is China's maritime behaviour. China's recent official statements and actions in what Beijing calls its --near seas -- represent a direct challenge to accepted interpretations of international law and established international norms," Willard said.
"While China does not make legal claims to this entire body of water, it does seek to restrict or exclude foreign, in particular, US, military maritime and air activities in the --near seas -- an area that roughly corresponds to the maritime area from the Chinese mainland out to the --first island chain--(described, generally, as a line through Japan, Taiwan, Philippines, and Indonesia) and including the Bohai Gulf, Yellow Sea, East China Sea, and South China Sea," he said.
Willard said Chinese naval and maritime law enforcement vessels have been assertive in recent years in trying to advance China's territorial claims in the South China and East China Seas which has resulted US partners and allies in East Asia seeking additional support and reassurance to balance and curb the Chinese behaviour.
"Unquestionably, China has made tremendous investment in its maritime capabilities across the board, to include the PLA navy. And we have no doubt that they have aspirations to make that a blue-water navy that they can deploy around the world, and they're demonstrating that today with anti-piracy operations in and near the Gulf of Aden," Willard said.
"They demonstrated it to a lesser extent by moving some of their surface fleet into the Mediterranean Sea during the Libya crisis in order to assist in evacuating Chinese citizens. So they are expanding their fleet, patrolling more, penetrating the first island chain and extending their operations further into the Pacific on a fairly steady pace," he said.
Willard said that many of China's maritime policy statements and claims stand in contrast to the United Nations Convention on the Law of the Sea (UNCLOS).
The US has consistently sought the appropriate balance between the interests of countries in controlling activities off their coasts with the interests of all countries in protecting freedom of navigation.
"China has questioned whether a non-party may assert such rights under UNCLOS, a baseless argument but one that would be removed if the US was a party to UNCLOS," he said.
Willard said China continues to accelerate its offensive air and missile developments without corresponding public clarification about how these forces will be utilised.
"Of particular concern is the expanding inventory of ballistic and cruise missiles (which include anti-ship capability) and the development of modern, fourth- and fifth-generation stealthy combat aircraft," he said.
"In conjunction, China is pursuing counter-space and cyber capabilities that can be used to not only disrupt US military operations, but also to threaten the space and cyber-based information infrastructure that enables international communications and commerce," Willard said.