Manila resorted to arbitration after more than a decade of unsuccessful regional attempts to forge a binding code of conduct in the sea, President Benigno Aquino III told reporters.
"We went through the arbitration because that is a means to resolve the dispute which is consistent with a peaceful policy and in conformity with international law," Aquino said.
The Philippines yesterday submitted to the tribunal in The Hague 4,000 pages of analysis and documentary evidence to defend its territorial claims, ignoring Beijing's warning the case will damage ties.
Hong said the Philippines agreed to China's position to settle disputes through direct negotiations in a series of bilateral documents and in a 2002 declaration signed by Beijing and the 10-member Association of Southeast Asian Nations on the conduct of parties in the South China Sea.
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"The Philippines is obliged to honor its own commitment," he said.
As a party to the UN Convention on the Law of Sea, China also declared in 2006 that such disputes are excluded from arbitration, Hong added.
That 2002 non-binding declaration on the South China Sea was seen as a first step to forging a binding agreement. China has only reluctantly agreed to open consultations and has lobbied some ASEAN members to prevent consensus.
Aquino expressed frustration that after more than a decade of talks between ASEAN and China "we still have no code of conduct."
"So what are our options with regards to the whole issue," he said. "I have to defend national territory and our sovereignty."
China, Brunei, Malaysia, the Philippines, Taiwan and Vietnam have overlapping claims across the busy South China Sea.