US President Barack Obama is attending a regional summit in Cambodia, with trade pacts and rumbling tensions over the South China Sea set to dominate.
The East Asia summit is part of regional Asean talks. Japanese, Chinese and Australian leaders are also there.
Mr Obama’s arrival on Monday came amid fractious debate on the maritime row between China and its Asian neighbours.
On Tuesday the US president met Chinese Premier Wen Jiabao but did not refer to the row in public comments.
The “co-operative and constructive approach” the US and China had taken to ties served both countries, Mr Obama said, but “clear rules of the road” were needed for international trade.
Mr Wen, for his part, said economic co-operation would be enhanced “as a means to tackle the difficulties we have and resolve the difference and disagreements between us”.
Both sides ignored shouted questions from reporters about the South China Sea, AFP news agency said.
China claims a U-shaped swathe of the South China Sea, including areas also claimed by Vietnam, the Philippines, Malaysia and Brunei.
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 last Asean (Association of South East Asian Nations) summit in July broke up acrimoniously, without a joint communique, with China facing accusations of using its clout to force host Cambodia to keep the territorial issue off the agenda.
The discord has continued at the latest summit. Cambodia said on Sunday that Asean nations had agreed not to “internationalise” the issue but negotiate on it as a bloc, something Beijing has been pushing for.
But on Monday, the Philippines – which has been boosting ties with the US – said no such accord had been reached and that it had “the inherent right to defend its national interests when deemed necessary”.
Japanese Prime Minister Yoshihiko Noda also raised security concerns in a meeting with Mr Obama. Japan is currently embroiled in a separate territorial dispute with Beijing over islands in the East China Sea.
“With the increasing severity of the security environment in East Asia, the importance of the Japan-US alliance is increasing,” Mr Noda said.
Discussions at the summit are also expected to focus on at least three free trade pacts in the region.
China, Japan and South Korea are scheduled to launch trade talks on Tuesday afternoon to discuss the possibility of a free-trade zone, Japanese and South Korean officials say.
Asean countries and China, Japan, South Korea, India, Australia and New Zealand are involved in the Regional Comprehensive Economic Partnership (RCEP) dialogue that seeks to strengthen regional trade.
The US is leading the Trans-Pacific Partnership (TPP) negotiations which currently involve four countries from Asean – Singapore, Brunei, Malaysia and Vietnam.
Mr Obama arrived in Cambodia from Burma, where he spent six hours meeting top leaders.
The first visit to the country by a serving US president, it was seen as a response to reforms initiated by the government of President Thein Sein.