China on Sunday sought to ease fears about its military ambitions and demanded respect from the international community as smaller neigbours accused it of behaving like a bully in the South China Sea.

Defence Minister Liang Guanglie told an annual security forum in Singapore that "democracy in international relations" and respect for "each other's core interests" were necessary to ensure "lasting peace, harmony and stability".

"I know many people tend to believe that with the growth of China's economy, China will become a military threat," said Liang, the first Chinese defence minister to attend the annual conference called the Shangri-La Dialogue.

"I would like to say that it is not our option," he said, adding that China would never "seek hegemony" or threaten any country.

Despite Liang's focus on respect and equality, his counterparts from the Philippines and Vietnam accused China of intimidating acts in the disputed Spratly and Paracel island groups in the South China Sea.

In a 45-minute speech followed by a question-and-answer session, Liang warned that countries "should not engage in any alliance targeting a third party" but did not go into detail.

He denied that Beijing was behind a spate of Internet attacks on foreign targets, and echoed calls made at the Singapore conference by the United States and Britain for international talks on promoting cyber-security.

"It is hard to attribute the real source of attacks and we need to work together to make sure that this security problem won't be a problem," Liang said, adding China itself suffered from widespread and frequent cyber-attacks.

On the sidelines of the forum, Liang held talks with outgoing US Defense Secretary Robert Gates on Friday, a meeting both sides described as positive.

Gates left Saturday for Afghanistan after delivering a speech warning of the danger of armed conflict in the South China Sea unless nations with conflicting claims adopt a mechanism to settle disputes peacefully.

After long-running tensions sparked by issues such as US arm sales to Taiwan, Liang said Sunday that "the picture of the bilateral relations between China and the United States is a good one".

"I believe all of us are very optimistic about the future of bilateral and military-to-military relations," he added.

Addressing the territorial disputes, Liang said China was committed to "peace and stability" in the South China Sea and insisted the situation "remains stable".

China, the Philippines, Taiwan, Brunei, Malaysia and Vietnam have all laid claim to overlapping sections of the territories, which are believed to hold major oil and gas deposits.

The Philippines accused China on Saturday of undermining peace and stability by sending naval vessels to intimidate Filipino fishermen and the crew of an oil exploration ship, as well as putting up posts and a buoy in Philippines-claimed areas in the Spratlys.

In May, Chinese surveillance ships confronted a Vietnamese oil exploration vessel between the Paracels and Spratlys. On Sunday, several hundred Vietnamese gathered for a rare protest in front of China's embassy in Hanoi.

In Singapore, Vietnam's Defence Minister Phung Quang Thanh urged China "to honour the policies that they announced" regarding the territorial disputes.

"I fully propose that we must exercise restraint and patience and commitment to solve these issues, these differences, by peaceful means," Thanh said.

Philippine Defence Secretary Voltaire Gazmin told the meeting that "actions by other states ... unnecessarily make other states like the Philippines worried and concerned".

Forum participants stressed the need to adhere to the Declaration on the Conduct of Parties in the South China Sea, a pact signed in 2002 by China and the 10-member Association of Southeast Asian Nations to prevent conflict until territorial disputes are resolved.