The United States has accused China of increased "provocations" against rival claimants to territory in the South China Sea and says its "aggressive and irresponsible behaviour" mean it is only a matter of time before a major incident or accident.
Jung Pak, deputy assistant secretary for east Asia at the US State Department, told a US think tank there was "a clear and upward trend of PRC provocations against South China Sea claimants and other states lawfully operating in the region," referring to the People's Republic of China.
She told the Center for Strategic and International Studies Chinese aircraft had increasingly engaged in unsafe intercepts of Australian aircraft in international airspace above the South China Sea and in three separate incidents in the last few months had challenged marine research and energy exploration activities within the exclusive economic zone of the Philippines.
Speaking later at the same event, Ely Ratner, assistant secretary of defence for Indo-Pacific Security Affairs, said there had been "dozens" of incidents in the first half of the year involving the Chinese military in the South China Sea, a sharp increase over the past five years.
"Beijing is systematically testing the limits of our collective resolve," he said.
"In my view, this aggressive and irresponsible behaviour represents one of the most significant threats to peace and stability in the region today, including in the South China Sea. And if the PLA continues this pattern of behaviour, it is only a matter of time before there is a major incident or accident in the region," he said, referring to China's armed forces.
The comments came ahead of an anticipated call between President Joe Biden and Chinese President Xi Jinping this week, which is expected to focus on ways to prevent the growing US-China strategic rivalry veering into conflict, particularly over the self-ruled Chinese-claimed island of Taiwan.
They also came ahead of meetings of Southeast Asian foreign ministers and partners, including the United States, next week in Cambodia.
China claims nearly all of the South China Sea and Pak called the claims "expansive and unlawful".
She added that China's "provocative actions" to implement such claims "contribute to regional instability, damage the economies of other claimant states, undermine the existing maritime order and threaten the rights and interests of all nations that rely on or operate in this vital waterway".
Pak said the US had a "very complicated relationship with Beijing" and was not trying to counter everything it was doing in Southeast Asia and the rest of the developing world.
"We want to make sure that countries, as they have their relationships with Beijing, have the tools and the power, and the and the ability to stand up for their autonomy and their sovereign decision making," she said.