WASHINGTON (AP) — The commander of U.S. forces in the Pacific said Tuesday the American military must be present in the South China Sea to ensure the security of sea lanes crucial to international trade.

The strong U.S. position on freedom of navigation in those disputed waters has become a source of friction with the principal regional power, China, which has conflicting territorial claims there with several neighbors.

Adm. Robert Willard said that China was less confrontational in 2011 in asserting its claims in the South China Sea than it was in 2010, when tensions rose between it and other claimant states, particularly the Philippines and Vietnam. Brunei, Malaysia and Taiwan also claim various small islands and atolls in those resource-rich waters.

But Willard said China continues to challenge vessels conducting oil and gas exploration within space that it claims as its own. "They remain aggressive," Willard told the Senate Armed Services Committee.

Willard, who retires this year, commands about 300,000 personnel in the U.S. Pacific Command, said China's military growth has continued "unabated" and its capabilities were advancing in all areas. He said the interests of the U.S. and its allies were being challenged in cyberspace, space and in maritime security in international waters around China.

He noted that the South China Sea carries some $5.3 trillion in regional commerce, $1.2 trillion of it American trade.

"The US military must be present there to ensure the security of those sea lines of comunication," Willard said.

He said China is not alone among the six claimants in making excessive territorial claims in the South China Sea but was unique in laying claim to "virtually all of it."

The U.S. irked China by announcing in 2010 that it had a national interest in the peaceful resolution of the South China Sea disputes, supporting efforts by Southeast Asian nations to negotiate as a group on the issue rather than bilaterally as Beijing would prefer.

China maintains that its military build-up is commensurate with its stature as a world power and it has no aggressive intentions. The Obama administration's recent strategic "pivot" to the Asia-Pacific has fueled Chinese suspicions that the U.S. wants to contain China's rise.

Willard said nations in the region were welcoming increased U.S. engagement but were asking how planned U.S. defense cuts would affect American force structure and military readiness.

The U.S. aims to cut $487 billion in defense spending over a decade to help reduce its vast national debt but says that it will not sacrifice its plans for a greater military presence in Asia.