US President Barack Obama is set to address the the contentious issue of the South China Sea at a summit dominated by rival claims to the strategically vital area.
The East Asian summit, which began the Cambodian captital of Phnom Penh on Sunday, forms part of the regional Association of South East Asian Nations (ASEAN) meeting with Chinese, Japanese and Australian leaders also in attendance.
Obama is expected on Tuesday to express concerns about the disputes between Beijing and its Southeast Asian neighbours, which have stoked tensions across the region this year and hampered efforts to foster economic co-operation.
US President Barack Obama believes there should be a reduction in tensions surrounding maritime territorial disputes in Asia, the White House said on Tuesday.
"There needs to be a lowering of tensions around these territorial disputes," Obama's deputy national security
adviser Ben Rhodes told reporters in Phnom Penh.
Obama is visiting Asia against a backdrop of diplomatic tensions between China and Japan and between China and several Southeast Asian nations over islands in the East China Sea and South China Sea.
Tensions have been high with Manila and Hanoi in recent months amid stand-offs and minor clashes around shoals and islands disputed with China.
The US president is on the final leg of a three-nation trip to Asia aimed at deepening Washington's influence in the region and countering the rise of China.
Obama arrived in Cambodia from Myanmar, where he spent six hours.
Both he and the outgoing Chinese Premier Wen Jiabao met for informal bilateral talks on the side.
Obama also was scheduled to have a one-on-one meeting with the Japanese Prime Minister Yoshihiko Noda.
Repeating a long-held Chinese position, Wen insisted on Monday that the maritime disputes should not be "internationalised" and discussed at multilateral events such as the summit.
China, which claims sovereignty over virtually all of the sea, prefers to negotiate directly with its neighbours from the 10-member Association of Southeast Asian Nations (ASEAN).
Al Jazeera's Marga Ortigas, reporting from Phnom Penh said:"There are internal grumblings at the summit, Cambodia does not want to discuss the maritime issues at the summit, Philippines and Vietnam are calling for Obama to discuss the South China seas, while China does not want to internationalise the dispute".
But Obama and ASEAN leaders agreed in a meeting on Monday to support a regional code of conduct to manage disputes over claims in the area, said a joint US-ASEAN communique.
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.
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, which would give Beijing an important diplomatic victory.
But the Philippines quickly denied that it had agreed, with President Benigno Aquino rebuking Cambodian Prime Minister Hun Sen during one of the meetings on Monday.
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.
Despite the tensions, leaders are expected to make progress on important economic issues on Tuesday.
ASEAN nations are set to officially launch negotiations to create an enormous free trade pact with China, Japan, India, South Korea, Australia and New Zealand.