A senior officer and military expert in China's People's Liberation Army has singled out Australia's role in the South China Sea, warning it should not "follow the United States blindly" and interfere in any territorial disputes.
Earlier this week, Washington's Centre for Strategic and International Studies said photos indicate Beijing is building a third airstrip on Mischief Reef, which lies in contested waters. 
Asked about the new airstrip, Senior Colonel Li Jie, a military expert at the PLA, said it was the US that had ratcheted up tension in the South China Sea, partly due to visits by American long-range bombers and refuelling tankers to Darwin.
"We need to understand why the US has deployed these in Australia," said Mr Li. "It is clear they are focused on the South China Sea and targeting China.
"I don't think any other countries can criticise China for building another runway," he added. "This is our backyard and we can decide what vegetables or flowers we want to grow."
President Xi Jinping is to visit to Washington next week, where China's construction of artificial islands is likely to be discussed.
Prime Minister Malcolm Turnbull is widely regarded as less wary than Tony Abbott of China's strategic ambitions but has been critical of Beijing's actions in the South China Sea. At the US-Australia dialogue in   January, he said: "there seems little doubt that the tough line on the disputed islands and reefs has been quite counterproductive".
"It has served to do no more than remind China's neighbours of the importance of a strong continuing American presence as a counterbalance to China," he said.
Beijing lays claim to the bulk of the South China Sea via its "nine-dash" line, a controversial and ambiguous marking on the map. But the area, which is a vital trade corridor and rich in oil, gas and fisheries, is subject to a complicated web of territorial disputes involving the Philippines, Vietnam, Malaysia, Brunei and Taiwan.
Last month, Foreign Minister Wang Yi said China had stopped its land reclamation in the Spratly Island chain amid increasing alarm about the scope and scale of construction in the area.
The CSIS said the new retaining wall on Mischief Reef mirrors early building work on two other reefs that became the foundation for a runway. The latest airstrip would be of particular concern to the Philippines, according to analyst Greg Poling. It is close to a ship that was deliberately grounded by the Philippines in 1999 and home to a contingent of its marines.
Asked about the new airstrip on Monday, a spokesman for the foreign ministry said China had "indisputable sovereignty" over what it calls the Nansha Islands and their adjacent waters, and that all construction was "lawful, reasonable and justified".
Jian Zhang, a senior lecturer at the University of NSW in Canberra who specialises in China security issues, said, "The facilities they are building are not necessarily useful in a military conflict. They could be destroyed or damaged relatively easily but they are useful for China to demonstrate and try and enforce their territorial claims in surrounding waters."
Australia's role in the debate over the South China Sea disputes was elevated in   May after a US defence official said B-1 bombers would be "placed" in Darwin as a countermeasure to "China's destabilising effect" on the region.
Both Canberra and Washington denied at the time that any specific agreement had been reached and said the official misspoke.
President Barack Obama announced in 2011 plans to rotate up to 2500 marines through an Australian training hub in Darwin as well as position equipment and supplies there.
While the US said it wouldn't create a permanent American military presence in Australia, the co-operation has been treated warily by Chinese officials.
Key pointsUS believes China is building a third airstrip in contested waters in South China Sea.
China has warned Australia not to interfere.