By RHEA SANDIQUE-CARLOS And JOSEPHINE CUNETA @ http://online.wsj.com/article/SB10001424127887324624404578257621131240336.html

MANILA—The Philippines is taking its territorial dispute with China to an international tribunal, raising the stakes in the political standoff among several countries with overlapping claims in the resource-rich South China Sea.

“The Philippines has exhausted almost all political and diplomatic avenues for a peaceful negotiated settlement of its maritime disputes with China,” Foreign Affairs Secretary Albert Del Rosario said Tuesday at a news conference, adding that the two countries have been expressing their views to each other since 1995 in attempt to settle the dispute.

“To this day, a solution is still elusive,” Mr. Del Rosario said.

He said the foreign-affairs department summoned Chinese Ambassador Ma Keqing on Tuesday afternoon and informed him that Manila is asking an international arbitration tribunal—provided for under the 1982 United Nations Convention on the Law of the Sea, or Unclos—to declare that China’s South China Sea claims are “unlawful” under the convention.

The Philippines hopes the tribunal will “achieve a peaceful and durable solution to the dispute over the West Philippine Sea,” Mr. Del Rosario said, using his country’s name for the area.

Beijing’s embassy in Manila quickly responded, saying China “has indisputable sovereignty over the islands in South China Sea and its adjacent waters.”

“The Chinese side strongly holds the disputes on South China Sea should be settled by parties concerned through negotiations. This is also the consensus reached by parties concerned in the Declaration on the Conduct of the Parties in the South China Sea,” the statement said. The declaration, signed in 2002 by China and the 10 member countries of the Association of Southeast Asian Nations, pledges to resolve disputes through direct negotiations.

A spokesman for China’s Foreign Ministry didn’t have an immediate comment Tuesday night. The ministry didn’t immediately respond to a list of questions faxed late in the afternoon.

Beijing is becoming increasingly assertive in its claims over large swaths of the South China Sea, including islands and shoals that are also claimed by Asean members Brunei, Malaysia, the Philippines and Vietnam, as well as Taiwan. The area has rich fishing grounds, vital shipping lanes, and potential reserves of oil and natural gas.

In recent years China’s government has built and occupied structures on reefs that are part of the Philippines’ continental shelf. Last February, two Chinese vessels blocked a Philippine ship that was conducting a seismic survey in the disputed area for London-based Forum Energy PLC, controlled by Philex Petroleum Corp.

The Philippines maintains a military garrison on one of the disputed islands, and the government has been referring to the South China Sea as the “West Philippine Sea” since last year.

Military ships from the two countries engaged in a two-month standoff early last year at Scarborough Shoal, about 120 nautical miles (220 kilometers) west of the Philippine island of Luzon. In June, China formally created a new administrative zone under its southern island province of Hainan, encompassing most of the disputed area on an official map within a line broken into nine sections.

Beijing also submitted a map with the controversial boundary, often called the “nine-dash line,” to the U.N. China then announced a law calling for the inspection, expulsion or detention of vessels entering its territory within the line.

Mr. Del Rosario said Tuesday that the maritime area within the nine-dash line includes parts of the Philippines’ continental shelf or the international seabed.

He said Manila will ask the tribunal to declare China’s claims within the line invalid, and to require that China bring its domestic laws into conformity with its Unclos obligations.

The Philippines will be represented at the tribunal by the country’s Solicitor General Francis Jardeleza and lead counsel Paul Reichler of U.S.-based law firm Foley and Hoag LLP.

“While we proceed with the legal track, the Philippines continues to exert all efforts to move forward and enhance its relations with China on the basis of mutual respect,” Mr. Del Rosario said.