Relations between the United States and China could hit another rough patch this week at Asia’s biggest security forum, where some participants will seek US help to thwart what they see as Beijing’s expansionism in the South China Sea.

US-China ties are already being tested. Beijing has reacted angrily to President Barack Obama’s meeting with the Dalai Lama at the weekend, calling it a violat-ion of its internal affairs, but stopped short of threatening retaliation.

That row comes only days before US Secretary of State Hillary Clinton heads to the Indonesian resort island of Bali for the annual Association of South East Asian Nations (ASEAN) Regional Forum. The meeting will focus on disputed atolls and islands in the oil-rich South China Sea, and China’s perceived muscle-flexing there.

“It could be a rough ARF,” Simon Tay, chairman of the Singapore Institute of International Affairs, said, referring to the forum. “The bilateral relationship has not been the best, and this will make it worse.”

Vietnam and the Philippines have accused China of acting aggressively over the past few weeks in asserting its claims to the strategically located and potentially lucrative waters, which straddle vital shipping lanes.

Both have been looking to Washington to support their case, while China is adamant about not involving other parties to help resolve the matter.

“Chinese leaders can’t be seen to be weak on this issue because of the backlash they will get within their country,” Ian Storey, a fellow at the Institute of Southeast Asian Studies in Singapore, said.

China, the Philippines, Malaysia, Brunei, Vietnam and Taiwan all claim parts of the South China Sea. China's claim is the largest.

ASEAN foreign ministers are likely to call for a long-awaited code of conduct for all parties in the South China Sea to be finalised by the end of this year.

“Things do not necessarily have to be this slow. We need to see some progress on the South China Sea,” Indonesian President Susilo Bambang Yudhoyono said while inaugurating the meeting.

“We need to send a strong signal to the world that the future of the South China Sea is a predictable, manageable and an optimistic one.”

Although some analysts say the South China Sea dispute could lead to an armed conflict, many feel that would not be in any party's interests.

China transports as much as 80 per cent of its oil imports through the South China Sea, and sends exports through the same waters to Europe, the Middle East and Africa.

“It is clearly in no country’s interest for the free flow of maritime trade through the South China Sea to be disrupted, and we are not nearly at that point yet,” Storey said.

Kao Kim Hourn, a secretary of state at the Ministry of Foreign Affairs, will lead Cambodia’s delegation to the summit.

Koy Kuong, spokesman for the Foreign Ministry, declined to weigh in directly on the South China Sea dispute, saying only that Cambodia hoped to see the issue settled according to the 2002 Declaration on the Conduct of Parties in the South China Sea, which was signed by China and members of the Association of Southeast Asian Nations at a 2002 ASEAN summit in Phnom Penh.

“We urge all relevant parties to implement the DOC … in order to move toward a peaceful resolution,” he said. “All ASEAN countries signed, along with China, on the issue of territorial integrity and sovereignty between China and Vietnam, the Philippines, Brunei and Malaysia.”

REUTERS. ADDITIONAL REPORTING BY VONG SOKHENG