By Stuart Grudgings and Lesley Wroughton
BANDAR SERI BEGAWAN, Oct 10 (Reuters) - U.S. Secretary of State John Kerry gave tacit backing to the Philippines' stance in a tense maritime dispute with China on Thursday, saying that all countries had a right to seek arbitration to resolve competing territorial claims.
The Philippines, a U.S. ally, has angered China by launching an arbitration case with the United Nations to challenge the legal validity of Beijing's sweeping claims over the resource-rich South China Sea.
The United States has refrained from taking sides in the dispute, one of Asia's biggest security headaches, but has expressed a national interest in freedom of navigation through one of the world's busiest shipping channels.
"All claimants have a responsibility to clarify and align their claims with international law. They can engage in arbitration and other means of peaceful negotiation," Kerry told leaders at the East Asia Summit in Brunei, including Chinese Premier Li Keqiang.
"Freedom of navigation and overflight is a linchpin of security in the Pacific," he added.
China claims almost the entire oil- and gas-rich South China Sea, overlapping with claims from Taiwan, Malaysia, Brunei, the Philippines and Vietnam. The last four are members of the 10-member Association of Southeast Asian Nations (ASEAN).
The row is one of the region's biggest flashpoints amid China's military build-up and the U.S. strategic "pivot" back to Asia signalled by the Obama administration in 2011.
Diplomatic efforts to ease tensions are now centred on Chinese talks with ASEAN to frame a code of conduct for disputes in the South China Sea, but Beijing has restricted talks to low-level consultations rather than formal negotiations.
The annual East Asia Summit ended on Thursday without significant progress on the dispute, with a joint ASEAN-China statement saying only that the two sides had agreed to "maintain the momentum of the regular official consultations".
Frustrated by the slow pace of regional diplomatic efforts to resolve the dispute, the Philippines has hired a crack international legal team to fight its unprecedented arbitration case under the United Nations' Convention on the Law of the Sea - ignoring growing pressure from Beijing to scrap the action.
Any result will be unenforceable, legal experts say, but will carry considerable moral and political weight.
Beijing has accused the Philippines of pursuing the case to legalise its occupation of islands in the disputed sea and said it would never agree to cooperate.
Some diplomats have expressed concern that the ASEAN-China consultations are a bid by China to delay a final agreement on a code while it expands its naval reach and consolidates its expansive claims.
ASEAN Secretary-General Le Luong Minh, in an interview with Reuters, insisted that the consultations that had their first round in China in September were a sign of progress.
"It's especially important progress if we look at what happened a year before," he said, referring to an unprecedented breakdown of an ASEAN summit in Cambodia over a failure to agree wording on the South China Sea.
The next round of talks will take place at an unspecified time next year, still at the relatively low "senior official" level.
On Wednesday, the United States and Japan - which has its own maritime dispute with Beijing - both pressured China to agree to abide by rules for the South China Sea, where Beijing has backed its claims with an increasingly assertive naval reach.
A Japanese official cited Prime Minister Shinzo Abe as telling Philippine President Benigno Aquino that Japan was "seriously concerned over efforts to alter the status quo by force, by intimidation or coercion".