In recent months, clashes have nearly erupted over overlapping claims in the sea, which lies on a major international shipping route.
China, which claims almost all of the energy-rich sea, does not want ASEAN involvement in negotiating or discussing the disputes.
U.S. President Barack Obama traveled to Thailand, Burma and Cambodia to meet with regional leaders and take part in the East Asia Summit.
US president's aims to reinforce Washington's 'Asia pivot' which has raised concerns in Beijing about greater US influence in region.
US president congratulates nation's move to civilian rule, release of hundreds of political prisoners and of loosening media restrictions.
President Barack Obama is using his first trip abroad since winning re-election earlier this month, to push for renewed U.S. interests on trade and economic development in Asia.
They had largely avoided bickering publicly through the media, until a statement late Sunday from ASEAN chair, Cambodia.
Security was tight, and traffic throughout the capital was blocked off, as leaders from around the world met in summits, sideline meetings and other venues, hosted by Cambodia.
Making history twice within hours, President Barack Obama today became the first U.S. president to set foot in Cambodia, a country once known for its Khmer Rouge "killing fields."