When Yao Yunzhu took the floor to reply to Pentagon chief Chuck Hagel's speech at an Asia-Pacific security forum, reporters relished the sense of déjà vu.

They wondered how the major general would question Hagel at the forum for the second year running.

The director of the Center for China-America Defense Relations at China's People's Liberation Army Academy of Military Science did not disappoint, rapidly firing four questions in fluent English and ignoring two attempts by the moderator to cut her off.

Yao, 60, said she was dissatisfied over not receiving direct or sufficient answers from Hagel on May 31 and not being given the chance to challenge his "wrong answers".

"During his speech, Hagel portrayed China as breaking the rules of the international community," Yao said.

"But you tell me which specific law China violated when it established an air defense identification zone in the East China Sea and which international laws the United States consulted when establishing its own ADIZ," she added as the three-day Shangri-La Dialogue ended in Singapore on Sunday.

The war of words between Yao and Hagel served as a sideshow amid tensions between China, the US and Japan at the forum over the situation in the East and South China seas.

The US and Japan felt perfectly at home when making blunt or veiled accusations against China, accusing it of "destabilizing" the two seas.

Yao said the South China Sea had not been a problem until recently when countries in the region had accelerated attempts to draw maritime baselines and to enlarge atolls to allow them to claim a 200-nautical mile exclusive economic zone around them.

Territorial claims by others only arose when rich oil and natural gas deposits were found and viewed by countries in the region as a potentially cheaper source of energy than that from the Middle East, Yao said.

The US Energy Information Administration estimates that the South China Sea contains about 11 billion barrels of oil and 190 trillion cubic feet of natural gas in proven and probable reserves.

Yao said another source of tension stemmed from the US accusing China of endangering freedom of maritime navigation and flights over the two seas whenever China opposed US military surveillance.

"This saw the US and some Southeast Asian countries finding a shared interest in jointly working against China," she said. "As a response to the increasing pressure, China has to stop setting the issue aside, as it used to do."

Yao called for a regional security framework that was more inclusive for China given that "such a big country does not want to challenge the leading role of the US but still needs to have its voice heard".

The alliance system with the US at its center was dominating the Asia-Pacific security framework, while Washington had not been clear enough about Beijing's role, she said.

Yao said she had prepared a question about Sino-US military cooperation for Hagel, but changed her mind after his remarks about China.

Yan Xuetong, dean of Tsinghua University's Institute of Modern International Relations, dismissed people's concerns that China's rise has not been peaceful and East Asia is on the brink of war.

Yan believes that East Asia has endured peace since 1991, longer than Europe which has had two wars since the Cold War, namely in Kosovo and Georgia.

"There has been no war in East Asia. Even today, the region, in my view, is still very peaceful," he said.

He said there might be accidents, but no danger of war in the region.

Many Chinese believe the US has been trying to take advantage of its alliance, a Cold War concept, in a bid to curtail China's growing influence in the region.

Chen Weihua contributed to this story.