Shanghai | US Defence Secretary Ashton Carter has singled out Australia as its partner in enforcing free passage through disputed areas of the South China Sea, drawing Canberra into an increasingly tense stand-off between Washington and Beijing over regional security.
During a speech at a high-profile conference in Singapore, Mr Carter said the US-Australia alliance was "more and more a global one". 
"As our two nations work together to uphold the freedom of navigation and overflight across the region, we're also accelerating the defeat of ISIL [Islamic State] together in Iraq and Syria," he said in a speech at the Shangri-La Dialogue.
He said both countries were part of a "principled security network" and, while that was not aimed at any particular country, "unfortunately there is growing anxiety in this region, and in this room, about China's activities on the seas, in cyberspace, and in the region's airspace".
"Indeed, in the South China Sea, China has taken some expansive and unprecedented actions that have generated concerns about China's strategic intentions," Mr Carter said.
The speech was energetically rejected by senior Chinese defence official Admiral Sun Jianguo, who criticised "some countries" for viewing China with a "cold war mentality and prejudice". In a meeting with Australian Defence Force chief Mark Binskin, Admiral Sun said Australia should take a "fair and objective stance" on the issue.
While Canberra has said it supports recent American sail-throughs and flyovers in the South China Sea, which are the subject of a web of complicated territorial disputes, so far it hasn't publicly participated in any joint operations.
Washington and Beijing, meanwhile, have clashed in recent weeks over US presence in the region, culminating in an incident in which two Chinese fighter jets carried out what the Pentagon said was an "unsafe" intercept of an American military reconnaissance aircraft.
"It's in America's interest to show that other countries are equally concerned about this issue," said Peter Jennings, executive director of the Australia Strategic Policy Institute, who was at the conference in Singapore.
"I think it was also a way for [Mr] Carter to say in a subtle way that Australia needs to do more and lift its game."
Australian Defence Minister Marise Payne did not attend the conference. She was campaigning in Townsville.
Asked to comment on Mr Carter's speech, Foreign Minister Julie Bishop said: "As the world becomes more connected and interdependent, the US-Australia alliance is necessarily an increasingly global one.
"Australia's position on disputes in the South China Sea is a longstanding one and is well known by all countries, including China," she said in an emailed statement.
The latest escalation in tensions comes at a crucial time for the region, amid speculation China is considering creating an air defence identification zone (ADIZ) above the South China Sea, under which it would require aircraft to identify themselves to Chinese authorities.
US Secretary of State John Kerry said on Sunday the declaration of such a zone would be seen as a "provocative and destabilising act" and urged Beijing not to act unilaterally.
When Beijing declared a similar zone in the East China Sea, over islands also claimed by Tokyo, it marked a diplomatic low-point for the China-Australia relationship. Ms Bishop called in the Chinese Ambassador to register her concern and was strongly criticised by Beijing.
The Shangri-La Dialogue was most likely the last regional security meeting before the Permanent Court of Arbitration in The Hague releases its ruling on challenges by the Philippines to China's maritime claims over much of the South China Sea.
The ruling, which is expected within weeks, could classify certain features in the disputed waters as islands or rocks, which has big implications for how much territory can be claimed and determine whether China's recent construction activities - building air strips, ports and storage facilities on top of reefs - is against the law.
The South China Sea, an important shipping lane, is subject to territorial disputes involving China, the Philippines, Vietnam, Malaysia, Brunei and Taiwan.
Mr Carter's comments come amid much debate in Australia about how to handle the alliance with the US.
Greens leader Richard Di Natale told the ABC on Sunday that if Republican Donald Trump won the American election there was "no better time . . to redefine the terms of the US alliance".
Mr Carter said the US was committed to its rebalancing to Asia and would "remain, for decades, the primary provider of regional security".