Wang Guanzhong, the highest ranking military official in the Chinese delegation at an Asia-Pacific security forum, started his speech on Sunday by highlighting the common aspiration for a utopia with the same name as the event: Shangri-La.

However, the deputy chief of the General Staff of the People's Liberation Army did not continue with his mild-toned comments as planned on the last day of the Shangri-La Dialogue in Singapore.

The lieutenant general diverted from the script about midway through the speech, saying he felt forced to respond to Tokyo and Washington's finger-pointing at China.

Japanese Prime Minister Shinzo Abe opened the forum on Friday night with a high-profile speech full of thinly veiled comments targeting China.

US Defense Secretary Chuck Hagel went further on Saturday by directly accusing China of "destabilizing" the South China Sea and by backing Tokyo's pursuit of a more muscular military role as a counterweight to Beijing.

"The speeches made by Mr Abe and Mr Hagel gave me the impression that they were coordinated with each other, they supported each other, they encouraged each other and they took the advantage of speaking first at the Shangri-La Dialogue and staged provocations and challenges against China," Wang told defense and military representatives and scholars from 27 countries.

Calling such rhetoric "unacceptable" and "unimaginable", Wang said: "China has never taken the first step to provoke trouble. China has only been forced to respond to the provocative actions by other parties."

When responding to the "nine-dash line" in the South China Sea, one of the many questions he received after the speech, Wang questioned the US motive for criticizing China, saying Washington should first abide by international laws by ratifying the United Nations Convention on the Law of the Sea, a document Beijing has ratified.

"When will the US ratify the UNCLOS?" Wang asked.

Wu Shicun, president of the National Institute for South China Sea Studies, said Wang sent a message that a growing China is not a threat to the world. On the contrary, it firmly safeguards regional stability.

Issues involving China, the US and Japan took center stage at the three-day meeting in Singapore.

Zhou Qi, a senior researcher at the Chinese Academy of Social Sciences, said Washington is using the territorial rows between China and the Philippines and Vietnam to challenge China and seek regional support for its Asian rebalancing policy.

Geoffrey Till, emeritus professor of maritime studies at King's College London, said the US is pursing "a very delicate balance" as it supports its allies obliged by treaties, but it also avoids to see conflicts in the region.

Despite the unusually strong language directed toward each other, Wang and Hagel dedicated part of their speeches to calling for improved military ties.

Lori Forman, a professor at the Asia-Pacific Center for Security Studies in the US, said open conversation is the key to managing differences and maintaining stability.

Wang also said he preferred Hagel's frankness by directly naming China, compared with Abe who did not mention any country, but obviously targeted Beijing.

"If I am to compare the attitude of the two leaders, I would prefer the attitude of Mr Hagel. It is better to be more direct," he said during the speech, drawing some laughter from the reporters.