The defence chiefs of China and the US engaged in a blunt exchange of words at an Asian security forum yesterday.
US Defence Secretary Chuck Hagel warned that Washington "will not look the other way" if Beijing seeks to restrict air traffic or freedom of navigation at sea.
Watch: US accuses China of 'destabilising' acts in South China Sea
PLA deputy chief of general staff Wang Guanzhong hit back, saying Hagel's speech at the Shangri-La Dialogue in Singapore was a "duet act" with Japanese Prime Minister Shinzo Abe, whose speech at the event on Friday attracted a similar retort from Beijing.
The exchange highlighted the growing tensions in East Asia, where increasingly aggressive behaviour by rival claimants to maritime territories is raising concerns.
Hagel accused China of destabilising the South China Sea, and gave a robust reassurance of America's commitment to the Asia-Pacific. Washington's rebalancing, or pivot, towards the region, he said, was not a promise, but "a reality".
"We also oppose any effort, by any nation, to restrict overflight or freedom of navigation, whether from military or civilian vessels, from countries big or small," Hagel said. "The United States will not look the other way when fundamental principles of the international order are being challenged."
In November, China declared an air defence zone over the East China Sea - without consulting its neighbours - and said foreign aircraft entering it must tell Chinese authorities their flight plans.
Ties between Washington and Beijing were strained last month when US prosecutors charged five PLA officers with cyberespionage. Hagel said the US would continue raising cybersecurity with China, "because dialogue is essential for reducing the risk of miscalculation and escalation in cyberspace".
A source close to the US government said there was pressure within the administration for Hagel to make stronger references to the cybersecurity issue. However, Yang Yujun, a spokesman for China's defence ministry, said the matter was not raised during a meeting yesterday between Hagel and Wang.
Speaking to Chinese media, Wang said Hagel's speech was "full of hegemony" and threats, and could cause instability in the region.
"Secretary Hagel's speech reminded me of Abe's speech last night. I feel that they are singing a duet," Wang said.
In his keynote speech on Friday night, Abe said Japan could play a more proactive security role in the region.
Wang told Hagel his speech was "more frank than he had expected". But he added: "Although I think your comments, or rather your criticisms, on China were groundless, frankly expressing your views is not necessarily a bad thing."