Chinese surveillance ships patrol in April 2012 near Scarborough Shoal, a reef claimed by the Philippines
The United States said it saw momentum in talks between China and Southeast Asia on agreeing to a code of conduct to ease deep friction over competing claims in the South China Sea.
The South China Sea is likely to be high on the agenda when US Secretary of State Hillary Clinton heads next month to Cambodia for talks of the Association of Southeast Asian Nations and regional powers including China.
Kurt Campbell, the US assistant secretary of state for East Asia, said he understood that a draft proposal on a code of conduct was being discussed and that the United States expected to hear more details while in Cambodia.
"What we have seen of late has been an increase in diplomacy between ASEAN and China about aspects associated with a potential code of conduct," Campbell told a conference at the Center for Strategic and International Studies.
"I will say that we are frankly impressed with the level of focus that particularly ASEAN has given to this," Campbell said.
Campbell did not give more details on the potential code of conduct and acknowledged that disputes over the South China Sea are "fraught with difficulty."
"They spur nationalist sentiment across the region as a whole and it is extraordinarily important to deal with them with great delicacy," he said.
ASEAN and China agreed in 2002 to negotiate a code of conduct. But there has been little visible progress, with a rising China preferring to negotiate with each country individually instead of dealing with a unified bloc.
ASEAN foreign ministers, meeting in April in Phnom Penh, said they hoped to narrow differences and sign a code of conduct with China by the end of the year.
The Philippines and Vietnam accuse China of aggressively asserting its claims in recent years, leading to minor clashes that diplomats and military commanders fear could quickly escalate into major conflicts.
The United States has recently expanded military relations with the Philippines and Vietnam, part of what President Barack Obama's administration has cast as a growing US focus on relations with Asia.
The details of the code of conduct remained murky. US Defense Secretary Leon Panetta, speaking to the annual Shangri-La Dialogue in Singapore on June 2, said the code should set a binding "rules-based framework" to prevent and manage disputes.
At the annual ASEAN talks in 2010 in Vietnam, Clinton said the United States had a "national interest" in open access to the South China Sea, through which half of the world's trade flows.
Her statement generated a wide response in Asia, with Southeast Asian nations largely welcoming the remarks and stepping up cooperation with the United States but China accusing her of fanning tensions.
Campbell said Clinton was also looking to visit Laos. If confirmed, the trip would be the first by a US secretary of state to Laos since the communist victory in 1975.
The United States established normal trade ties with Laos in 2004 and has been studying ways to clean up ordnance. The United States dropped millions of bombs on Laos during the Vietnam War to cut off Hanoi's supply lines.
US relations with Laos have remained uneasy largely due to concerns over treatment of the Hmong, a hill people who assisted US forces during the Vietnam War and have since reported incidents of persecution.
Campbell and the Laotian vice foreign minister, Bounkeut Sangsomsak, met Wednesday in Washington and discussed cooperation on issues including health, education, law enforcement and anti-trafficking, the State Department said.
One signature effort of the Obama administration has been reaching out to another long-isolated nation -- Myanmar.
The country formerly known as Burma has undertaken dramatic reforms since last year including allowing elections in which opposition icon Aung San Suu Kyi won a seat in parliament.
US senators said Wednesday that they expected soon to confirm Derek Mitchell as the first US ambassador to Myanmar in more than 20 years.