PHNOM PENH: US President Barack Obama on Tuesday defied Chinese protests and raised concerns at a summit about territorial disputes that have sent diplomatic and trade shockwaves across the region.

Obama weighed into the debate over China's sweeping claims to the South China Sea, which have rattled less powerful Southeast Asian countries, as well as a separate rift between Beijing and Tokyo over islands in the East China Sea.

“I think President Obama's message is there needs to be a reduction of the tensions... to ensure that these types of disputes don't risk escalation,” Ben Rhodes, a senior aide to the president, told reporters.

In response to concerns raised by Obama and other leaders at the 18-nation East Asia Summit in Cambodia, Chinese Premier Wen Jiabao issued a stern admonishment of China's critics and a strong defence of his country's claims.

“We do not want to bring the disputes to an occasion like this,” Wen told Obama and the other leaders in one of the final sessions of the two-day event, according to Chinese vice foreign minister Fu Ying.

“China's act of defending its sovereignty is necessary and legitimate...and we have properly handled the incidents that were not of the making of China.” Obama’s visit to Cambodia was the final leg of a three-nation trip to Southeast Asia — the first foreign tour since his re-election — aimed at deepening Washington's influence in the region and countering the rise of China.

He began in Thailand, then made a lightning and historic visit to Myanmar, a former military-ruled country that was closely aligned to China but which is undergoing dramatic political reforms.

Obama departed Phnom Penh on Tuesday night for the United States.

China, which claims sovereignty over virtually all of the South China Sea, prefers to negotiate directly with its neighbours from the 10-member Association of Southeast Asian Nations (Asean).

Asean members Vietnam, the Philippines, Malaysia and Brunei, as well as Taiwan, also have claims to parts of the sea, which is home to some of the world's most important shipping lanes and believed to be rich in fossil fuels.

The rival claims have for decades made the sea a powder keg issue in the region. Chinese and Vietnamese forces engaged in clashes in 1974 and 1988 in which dozens of troops died.

After a long period of relative calm, tensions have risen over the past two years, with the Philippines and Vietnam expressing concerns that China is becoming increasingly aggressive in staking its claims.

Some bruising diplomatic confrontations this year have overshadowed regional meetings at which participants typically prefer to focus on improving economic ties.

At the East Asia Summit, the first day was dominated by infighting over the issue among the Asean bloc.

Cambodia, this year's Asean chair and a close Chinese ally, said the 10 nations had agreed not to “internationalise” the disputes.

This would have given China an important diplomatic victory and potentially muzzled Obama on the issue in Cambodia.

But the Philippines quickly denied this had been agreed, with President Benigno Aquino rebuking Cambodian Prime Minister Hun Sen during one of the meetings on Monday.

“How can there be a consensus? A consensus means 100 per cent. How can there be a consensus when two of us are saying we're not with it,” Philippine Foreign Secretary Albert del Rosario told reporters afterwards.

He said later the other country that did not agree was Vietnam.

The feud echoed unprecedented infighting at an Asean foreign ministers’ meeting in Phnom Penh in July, which ended for the first time in the bloc’s 45-year history without a joint communique.

The Philippines and Vietnam had wanted the statement to make specific reference to their disputes with China, but Cambodia blocked the moves.

Despite the tensions, leaders made progress on important economic issues on Tuesday.

Asean nations officially launched negotiations to create an enormous free trade pact with China, Japan, India, South Korea, Australia and New Zealand.

Trade ministers from China, Japan and South Korea also kick-started three-way free trade negotiations.—AFP