Opening a new source of potential friction with China, the Obama administration said Friday that it would step into a tangled dispute between China and its smaller Asian neighbors over a string of strategically significant islands in the South China Sea.
Secretary of State Hillary Rodham Clinton, speaking at an Asian regional security meeting in Vietnam, stressed that the United States remained neutral on which regional countries had stronger territorial claims to the islands. But she said that the United States had an interest in preserving free shipping in the area and that it would be willing to facilitate multilateral talks on the issue.
Though presented as an offer to help ease tensions, the stance amounts to a sharp rebuke to China. Beijing has insisted for years that all the islands belong to China and that any disputes should be resolved by China. In March, senior Chinese officials pointedly warned their American counterparts that they would brook no interference in the South China Sea, which they called part of the “core interest” of sovereignty.
Many of the islands are just rocks or spits of sand, but they are rich in oil and natural gas deposits, and China views them as important outposts that extend its territorial waters far into the busy shipping lanes in the sea.
“The United States has a national interest in freedom of navigation, open access to Asia’s maritime commons and respect for international law in the South China Sea,” Mrs. Clinton said.
The announcement was a significant victory for the Vietnamese, who have had deadly clashes in past decades with China over some of the islands. Vietnam’s strategy has been to try to “internationalize” the disputes by bringing in other players for multilateral negotiations.
The administration’s decision to get involved appeared to catch China flat-footed and angered its foreign minister, Yang Jiechi, at a time when the country is already on edge over naval exercises the United States and South Korea will hold starting this weekend off the Korean Peninsula.
Twelve of the 27 countries at the security meeting spoke out in favor of a new approach to the South China Sea, prompting Mr. Yang to observe that the American effort seemed orchestrated.
International concern has been deepening about China’s maritime ambitions, which have expanded with its economic and military muscle. China raised tensions with Vietnam this year with plans to develop tourism in one of the island groups, the Paracels, which the two nations fought over in 1974 before China assumed full control. They had another lethal clash in 1988 over the Spratly island group.
In recent months, administration officials said, China has harassed fishing boats and leaned on energy companies that have tried to make offshore deals with other countries.
Although American relations with China on political and economic matters are regarded as stable, military ties have become strained over United States arms sales to Taiwan and American concerns about China’s growing naval ambitions. In June, China withdrew an invitation to host a visit by Defense Secretary Robert M. Gates, and the two have largely suspended regular military-to-military talks.
This week, China was already bristling over the joint American-South Korean naval exercises because some drills are to take place in the Yellow Sea, which China claims as a military operation zone.
At the security meeting, other tensions flared on the familiar front of North Korea, with a North Korean official threatening a “physical response” to the naval exercises. The United States made no secret that it intended the drills to be a deterrent to North Korean aggression. It announced them after an investigation led by South Korea found the North responsible for torpedoing a South Korean ship, the Cheonan, in March.
The North Korean official, Ri Tong-il, said, “This is not defensive training,” noting that the United States was deploying one of its most formidable nuclear-powered aircraft carriers, the George Washington, in the exercises. “It is a grave threat to the Korean Peninsula and also to the region of Asia as a whole.”
But North Korea has opened a small window of engagement on the issue. Military officers from North Korea and the United Nations Command met on the inter-Korean border on Friday for the second time this month to discuss the sinking. Meeting at the border village of Panmunjom, colonels from both sides “exchanged ideas and further details for convening a joint assessment group” to investigate “the cause of the armistice violations that led to the sinking,” the American-led United Nations Command said.
It remained unclear whether North Korea accepted the proposal. North Korea has so far insisted that it conduct its own investigation by sending a team of “inspectors” to South Korea.
On Friday, the United Nations Command notified North Korea of plans to hold another joint America and South Korean military exercise: an annual drill from Aug. 16 to Aug. 26. As is normal for the annual drill, no location was announced.
Mrs. Clinton’s stop in Hanoi wrapped up a grueling trip that amounted to a tour of American wars, past and present: from Afghanistan to the demilitarized zone in South Korea, and finally to Vietnam, where, in a sunset ceremony, she watched the remains of three American soldiers killed in the war placed on an Air Force transport plane to be returned to the United States.
Mrs. Clinton sought to apply lessons from the American experience in the Korean War to Afghanistan. “We saw South Korea struggle to become a functioning democracy — huge amounts of instability, coups, corruption, scandal, you name it,” she said. “It’s good to remind ourselves: the United States has stood with countries that went through a lot of ups and downs for a lot longer than eight years.”