Philippine Foreign Secretary Albert del Rosario is expected to announce at 2:30 pm that Manila has filed a formal plea before the UN arbitration tribunal, officials said, despite Chinese warnings of a fallout in bilateral relations.
"In all of this, the Philippines... Will do what is right. China can do what it prefers to do on this matter," President Benigno Aquino's spokeswoman Abigail Valte told reporters yesterday.
The two-hour stand-off in the Spratly archipelago was the latest in a series of escalations in a dispute between the two countries over their competing claims to waters and islands close to Philippine landmass.
China's claims over the strategically important South China Sea, believed to contain vast oil and gas reserves, overlap those of the Philippines as well as Brunei, Malaysia, Vietnam and Taiwan.
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The Philippine case argues that China's claims cover areas as far as 870 nautical miles (1,611 kilometres) from the nearest Chinese coast, and are thus illegal under the UN Convention on the Law of the Sea.
Yesterday's incident took place at Second Thomas Shoal, where a small number of Filipino soldiers are stationed on a Navy vessel that was grounded there in 1999 to assert the Philippines' sovereignty.
China had said its coastguard successfully turned away a similar Filipino attempt on March 9.
The Philippine foreign department said its plea to the UN would argue the disputed areas, including the Second Thomas Shoal, are part of the Philippines' continental shelf over which Manila has sole sovereign rights and jurisdiction.