Secretary of State Hillary Clinton yesterday said the Pacific "is big enough for all of us" as the United States pushes for a more visible military role across the region to counter China.
Meanwhile, US Defense Secretary Leon Panetta yesterday pledged a defence deal with Thailand in Bangkok amid a once in a decade leadership change in China.
In a speech at a marine defence hub in the South Australian capital Adelaide, America's top diplomat sought to allay fears about Washington's pivot into Asia, which has irked Beijing.
She called Australia an "indispensable" ally and said both Canberra and Washington wanted to strengthen ties with China and other nations in the region, in what she called "the Pacific century".
Hillary said Australia's relationship with the United States should be seen as complementary to its ties in Asia, particularly China which is Canberra's biggest trading partner.
"We support Australia having strong, multi-faceted ties with every nation in the Asia-Pacific, indeed in the world, including China, just as we seek the same," she said.
"And I have said repeatedly, the Pacific is big enough for all of us."
In Bangkok, US and Thailand pledged to renew their military alliance for a new security era.
The last time the two nations drafted such a joint declaration was in 1962, when the United States promised to defend Thailand from "communist aggression".
Although the new statement made no reference to China's rising military power, Washington's strategic tilt to the Asia-Pacific is meant to offset Beijing's clout and maintain American influence there.