By Greg Torode and Manuel Mogato
HONG KONG/MANILA (Reuters) - The Philippines will file a case against China over the disputed South China Sea at an arbitration tribunal in The Hague next week, subjecting Beijing to international legal scrutiny over the increasingly tense waters for the first time.
Manila is seeking a ruling to confirm its right to exploit the waters in its 200-nautical mile exclusive economic zone (EEZ) as allowed under the U.N. Convention on the Law of the Sea (UNCLOS), its team of U.S. and British lawyers said.
A ruling against China by the five-member panel of the Permanent Court of Arbitration could prompt other claimants to challenge Beijing, experts said. But while legally binding, any ruling would effectively be unenforceable as there is no body under UNCLOS to police such decisions, legal experts said.
China, which has refused to participate in the case, claims about 90 percent of the South China Sea, displaying its reach on official maps with a so-called nine-dash line that stretches deep into the maritime heart of Southeast Asia.
The Philippines, Vietnam, Malaysia, Brunei and Taiwan also have claims to parts of the potentially energy-rich waters.
The U.N. convention gives a country 12 nautical miles of territorial control with claim to sovereign rights to explore, exploit and manage natural resources within 200 miles. China claims several reefs and shoals in Manila's EEZ.
The head of the Philippines' legal team, Paul Reichler, a lawyer at U.S. law firm Foley Hoag, told Reuters a submission would be sent electronically on Sunday, meeting a March 30 deadline set by the tribunal. Manila filed an initial complaint in January 2013.
Legal experts said it could take months for the panel to weigh the case.
Diplomats and experts who follow the tensions in the South China Sea said Manila was going ahead despite pressure from China to delay or drop its submission.
"They've crossed a significant line here ... the pressure to withdraw before actually mounting an argument has been intense but they've stayed the course," said Carl Thayer, from the Australian Defence Force Academy in Canberra.
Arbitration would clarify Manila's rights to fishing and other resources in its EEZ as well as rights to enforce its laws in those areas, Philippine Foreign Affairs Secretary Albert del Rosario said.
"We see arbitration as an open, friendly and durable solution to the dispute," del Rosario told a business forum recently.
China reiterated this week that it would not take part.
"We demand the Philippines ends it mistaken actions and stop going further down this wrong path to prevent bilateral relations from being further harmed," Foreign Ministry spokesman Hong Lei told a news briefing on Wednesday.
"China's determination and resolve to protect its sovereignty and territorial integrity is unwavering."
Diplomats said the case was the focus of growing interest across East Asia and beyond given China's assertiveness in both the South and East China Seas.
Washington has stiffened its rhetorical support for Manila's action, even as it insists it does not take sides in regional territorial disputes.
The State Department warned this month of the "ambiguity" of some claims to the South China Sea and called for disputes to be solved legally and peacefully, through means such as arbitration.
Tensions have been on full display in recent weeks.
Earlier this month, Manila protested action by Chinese coastguard ships to block two Philippine civilian vessels resupplying marines on the disputed Second Thomas Reef.
The Philippines instead air-dropped supplies to the marines, who live on an old military transport ship rammed onto the reef in 1999 to mark Manila's territory. While Chinese vessels regularly surround the reef, it was the first time China had blocked a routine re-supply mission, a move Thayer said could have been related to the arbitration case.
Further north, the two sides have traded angry words over the Scarborough Shoal, where in January Philippine officials said a Chinese coastguard ship fired water cannon at Filipino fishermen.
Manila says both reefs lie within its EEZ. China says they are part of its territory.
Much further to the south, Chinese naval ships staged exercises in January at the James Shoal, a submerged reef within Malaysia's EEZ.
Less visibly, China has applied pressure behind the scenes, attempting to isolate the Philippines within the Association of South East Asian Nations (ASEAN), one regional diplomat said.
"China has let us all know that they are very angry ... The message is clear - you must not support this in any way," said the envoy, who declined to be identified because of the sensitivity of the issue.
Diplomatic sources in Vietnam have told Reuters that China put pressure on Hanoi over joining the case at the tribunal. A Vietnamese Foreign Ministry spokesman last month said Hanoi reserved the right to apply "all necessary and appropriate peaceful means" to protect its sovereignty.
Malaysian officials have given no indication they are planning to join the action or launch their own case.
(Additional reporting by Ben Blanchard in Beijing and Stuart Grudgings in Kuala Lumpur. Editing by Dean Yates)