Tension in the South China Sea is expected to top the agenda for a regional Asean forum this week.
China and several countries in the 10-nation bloc are laying claim to disputed waters in the area.
Foreign ministers of the group are meeting in Cambodia before the arrival of their regional counterparts from 16 countries, including China.
US Secretary of State Hilary Clinton will also join the meeting in Phnom Penh later in the week.
Mrs Clinton, who will be leading a trade delegation, has called for ''progress'' on a code of conduct for the South China Sea, signalling the United States' interest in the geopolitical tension in the region.
Speaking to reporters in Tokyo on Sunday, she urged China and Asean nations "to resolve their disputes without coercion, without intimidation, without threats and without conflict".
The Philippines has been leading the charge for Asean to pressure China to accept the code of conduct.
A maritime stand-off between China and the Philippines developed in a reef area known as the Scaborough Shoal in April, with China denying reports it was preparing for war at the height of the tension in May.
Both sides accused the other of intruding into territorial waters.
Vietnam was also angered by a recent call from China for oil exploration bids in disputed territory.
China has overlapping territorial claims with several Asean members - the Philippines, Vietnam, Malaysia and Brunei - in the resource rich area.
But Asean's members are divided over what to do. The four affected countries want action but others, like Cambodia, are grateful recipients of Chinese aid and investment, and reluctant to rock the boat, says the BBC's Guy DeLauney.
Asean was set up in 1967 by founder members Thailand, Indonesia, Malaysia, the Philippines and Singapore. Brunei joined in 1984, followed by Vietnam in 1995, Laos and Burma in 1997 and Cambodia in 1999.
