United States Defence Secretary Lloyd Austin says China's recent "dangerous" behaviour towards Royal Australian Air Force planes should "worry us all".
He was addressing an international summit in Singapore.
Earlier this year, a RAAF surveillance plane was targeted with a laser shone from a Chinese navy ship as the aircraft flew over the Arafura Sea, north of Australia.
Last month, a Chinese fighter jet intercepted another Australian surveillance plane as it flew over the South China sea, releasing a flare and dropping a load of aluminium chaff, some of which was sucked into the plane's engines.
The Australian government has complained about both incidents, accusing the People's Liberation Army (PLA) of putting the lives of Australian servicemen and women at risk.
The comments have been received a frosty reception from Beijing, which has accused Australia of being in the wrong.
Mr Austin, a former US army general, said there had been "an alarming increase in the number of unsafe aerial intercepts and confrontations at sea by PLA aircraft and vessels".
"The stakes are especially stark in the Taiwan Strait."
The defence chief insisted the US and its allies would not be deterred by Beijing's "more coercive and aggressive approach to its territorial claims".
"And we'll do so right alongside our partners, and we'll continue to be candid about the challenges that we all face.
Mr Austin met with China's Defence Minister, Wei Fenghe, for the first time on the sidelines of the summit.
Mr Wei warned the United States there would be war if Taiwan sought independence from China.
"Our policy on Taiwan has not changed," Mr Austin said.
"We remain committed to a One China policy, and we also remain committed to providing Taiwan with the military means to defend itself.
"I know that countries across the region and across the globe are really focused on this issue."
Australian Defence Minister Richard Marles, who met with Mr Austin at the summit, was also questioned about aggression with regards to Taiwan.
"In terms of Australia's involvement, all we would seek to do was play whatever role we could in facilitating that."
Mr Marles, who was criticised extensively by the Coalition during the recent election campaign for what it said was his wavering on China, said the new federal government's position was clear.
"China remains Australia's largest trading partner; China's economic success is connected to that of our own and the region.
"So Australia's approach will be anchored in a resolve to safeguard our national interest, and our support for regional security and stability based on rules."
Meanwhile, Lieutenant General Zhang Zhenzhong, a senior Chinese military officer, called Mr Austin's speech a "confrontation".
"There were many unfounded accusations against China," he said.
"We expressed our strong dissatisfaction and firm opposition to these false accusations," Lieutenant General Zhang, vice chief of the joint staff department of China's Central Military Commission, told reporters.
"The United States is trying to form a small circle in the Asia-Pacific region by roping in some countries to incite against some other countries. What should we call this other than confrontation?"
ABC/Reuters
