(Adds reaction from China's ambassador in Manila)
MANILA, Jan 22 (Reuters) - The Philippines has asked an international tribunal to intervene in its longstanding South China Sea territorial dispute with China and declare that Beijing's claims are invalid, the government said on Tuesday.
Manila asked the tribunal of the U.N. Convention on the Law of the Sea (UNCLOS) to order a halt to China's activities that the Philippines says violates the Southeast Asian nation's sovereignty.
China's claims over islands, reefs and atolls in resource-rich waters off its south coast and to the east of mainland Southeast Asia set it directly against U.S. allies Vietnam and the Philippines, while Brunei, Taiwan and Malaysia also lay claim to parts.
"The Philippines has exhausted almost all political and diplomatic avenues for a peaceful negotiated settlement of its maritime dispute with China," Foreign Affairs Secretary Albert Del Rosario told reporters.
"To this day, a solution is still elusive. We hope that the arbitral proceedings shall bring this dispute to a durable solution," he said.
But it was not clear how the tribunal can help. While all its decisions are binding on countries concerned, it has no power to enforce them.
China, in response, restated its claims to the territory and dismissed any need for external intervention.
State news agency Xinhua quoted Ma Keqing, China's ambassador to the Philippines, as saying that China "has indisputable sovereignty" over the South China Sea islands and adjacent waters.
"The Chinese side strongly holds that the disputes on the South China Sea should be settled by parties concerned through negotiations," Ma was quoted as saying after meeting a senior Philippine diplomat.
The Philippines has previously sought the support of the Association of Southeast Asian Nations (ASEAN) on the territorial dispute, with ASEAN agreeing to ask China to start talks on a code of conduct.
But Beijing says it wants to address the disputes via bilateral talks. Its relations with Tokyo are also under strain after the Japanese government bought disputed islands from a private Japanese owner in September, triggering violent protests and calls for boycotts of Japanese products across China.
Manila said that any joint development with China should respect Philippine laws. A unit of Philippine firm Philex Petroleum Corp is hoping to resume talks with Chinese state-owned offshore oil producer CNOOC on joint exploration of oil and gas fields in the South China Sea.
(Reporting by Rosemarie Francisco in MANILA and Koh Gui Qing in BEIJING; Editing by Nick Macfie and Ron Popeski)