Eyeing Beijing's assertiveness, US President Barack Obama and the prime ministers of Japan and Australia have committed to deepen their military cooperation and work together on strengthening maritime security in the Asia-Pacific region.
The meeting, the first since 2007 among leaders of the three allies, risked antagonising Beijing after a week when Obama reached a surprising level of consensus with President Xi Jinping on climate change and trade, and Japan and China took steps to improve their relationship.
China has viewed Obama's efforts to deepen alliances with other countries in the region, particularly on security issues, as an attempt to counter Beijing's rise.
In a joint statement following the meeting, the three leaders said they had agreed to "deepen the already strong security and defence cooperation" between their countries. They also agreed to work on boosting "maritime security capacity building" in a region rife with disputes between China and its neighbours over claims to waters and islands.
However, there were no announcements on specific military exercises or new troop deployments within the region.
White House officials insisted that the three-way talks on the sidelines of the Group of 20 economic summit were not meant to send a message to China. But in advance of Obama's meeting with Australian Prime Minister Tony Abbott and Japan's Shinzo Abe, the US president pressed China to "adhere to the same rules as other nations - whether in trade or on the seas."
"By virtue of its size and its remarkable growth, China will inevitably play a critical role in the future of this region," Obama said on Saturday in a speech at the University of Queensland. "And the question is, what kind of role will it play?"
An Obama administration official said the three-way meeting had been in the works for a year. Beyond military cooperation, the leaders also discussed the US-led campaign to defeat Islamic State militants in the Middle East, combat the spread of the deadly Ebola virus in West Africa and stop Russia's destabilising actions in Ukraine.
Australia was Obama's last stop on a week-long trip that began in China and Myanmar. He arrived politically weakened at home by the Democratic Party's election defeats on November 4. The president has tried to show the region's leaders that he retains the ability to deliver on promises to deepen US engagement in Asia and the Pacific, an effort he sees as a central part of his foreign policy.
"There are times when people have been sceptical of this rebalance, they're wondering whether America has the staying power to sustain it," Obama said. "I'm here to say that American leadership in the Asia-Pacific will always be a fundamental focus of my foreign policy."
In China, he emerged with an ambitious agreement to reduce greenhouse gas emissions, as well as a deal to extend the validity of visas.
· Wary of a more muscular Russia and China, US Defence Secretary Chuck Hagel said the Pentagon would make a new push for fresh thinking and creative ideas about how the US could keep and extend its military superiority despite tighter budgets and 13 years of war. Hagel announced a "defence innovation initiative" that he likened to historic and successful campaigns during the cold war to offset military advantages of US adversaries. South China Morning Post