US President Barak Obama and Australian Prime Minister Julia Gillard have announced plans to station US troops in Australia from next year.
Initially 250 marines will be stationed in the Northern Territory, increasing to 2,500 troops in the next few years.
The move is seen as a more assertive role for the US in the Asia-Pacific, particularly to counter the influence of China in the region.
Mr Obama said the US was "stepping up its commitment to the entire Asia-Pacific", including China.
"The main message that I've said, not only publicly but also privately to China, is that with their rise comes increased responsibility," he said.
"It is important for them to play by the rules of the road."
China has expressed unease over the deployment.
Chinese foreign ministry spokesperson Liu Weimin said to the AFP news agency: "It may not be quite appropriate to intensify and expand military alliances and may not be in the interest of countries within this region,"
"The United States is also trying to get involved in a number of regional maritime disputes, some of which concern China's sovereignty and territorial integrity," a commentary from China's official Xinhua news agency said.
Tensions in the South China Sea, which is claimed by several nations, including China, Vietnam and the Philippines, are thought to be one of the reasons of regional concern for the US.