The Philippines raised the stakes in its maritime territorial dispute with China by announcing Tuesday it is taking the case to an international tribunal.
The two Asian nations have been at loggerheads over China's claims of sovereignty over large swathes of the South China Sea, one of several tense disagreements between Beijing and its neighbors over waters in the region.
"The Philippines has exhausted almost all political and diplomatic avenues for a peaceful negotiated settlement of its maritime dispute with China," Philippine Foreign Minister Albert del Rosario said Tuesday.
As a result, Manila is challenging China's claims, which include the waters off the west coast of the Philippines, at an international arbitration tribunal, citing the United Nations Convention on the Law of the Sea.
The state-run Chinese news agency reported the announcement by the Philippines on Tuesday but didn't carry an immediate response from Beijing.
Other countries, like Vietnam and Malaysia, also lay claim to parts of the South China Sea, a 1.3 million square-mile patch of the Pacific Ocean dotted with hundreds of largely uninhabited islands and coral atolls.
The area is a fertile fishing ground and is believed to hold large oil and gas reserves under its seabed.
Tensions between China and the Philippines soared last year during a naval standoff over a remote rocky outcrop in a disputed part of the sea. That crisis lasted months and stoked fears of an open conflict before the Philippines withdrew its ships, citing stormy weather.
Analysts say China is trying to solidify its claims of "indisputable sovereignty" over most of the South China Sea by conducting regular maritime patrols in the area.
It is using a similar approach in its heated dispute with Japan over set of small islands in the East China Sea.
The United States is treading a delicate path amid the various territorial tensions in the region.
On Sunday, Chinese Foreign Ministry Spokesman Qin Gang warned United States to "be careful with its words" after Secretary of State Hillary Clinton said Washington opposes "any unilateral actions that would seek to undermine Japanese administration" of the disputed islands in the East China Sea.
Clinton had reiterated the U.S. policy that it doesn't take a position on the ultimate sovereignty of the islands.
As recently as last week, Xinhua reported that Chinese surveillance vessels were carrying out regular missions in the South China Sea.
The Xinhua report cited Liu Cigui, director of the State Oceanic Administration, as saying that China would continue the patrols "to secure the nation's maritime rights and interests" in areas it claims as its territorial waters.