Following the US statement to increase freedom-of-navigation operations over the South China Sea, China accused the U.S.-allied Philippines of "political provocation" in seeking international arbitration.
Chinese Foreign Minister Wang Yi said the decision by Philippine leaders to lodge a case with a tribunal in The Hague was "irresponsible to the Filipino people and the future of the Philippines."
China has refused to participate in the arbitration process, which it has denounced as illegitimate.
Wang said that China is prepared to negotiate yet Philippines refused the deal.
Meanwhile, Admiral Harry Harris, head of the U.S. Navy's Pacific Command, told a hearing of the House of Representatives Armed Services Committee, "We will be doing them more, and we'll be doing them with greater complexity in the future and ... we'll fly, sail and operate wherever international law allows."
"We must continue to operate in the South China Sea to demonstrate that water space and the air above it is international," Harris added.
He contended that China was changing the operational landscape in the South China Sea by deploying missile and radar as part of an effort to military to dominate East Asia.
In 2013, the Philippines initiated arbitration after Beijing refused to withdraw its ships from a disputed shoal under a U.S.-brokered deal.
Philippines argued that China's massive territorial claims in the strategic waters do not conform with 1982 U.N. Convention on the Law of the Sea and should be declared invalid. Some Chinese-occupied reefs and shoals do not generate, or create a claim to, territorial waters.
A ruling is expected later this year, after the tribunal decided last October that it could hear the case.
In commemoration of the Philippine's People Power, more than 100 protesters gathered to call on China to withdraw from the disputed Spratly and Paracel Islands. They demanded China stop its militarization of the South China Sea demonstrated outside Beijing's consulate.
One demonstrator said, "If there will be no outrage, if they won't be stopped in the Woody Island, then they will also deploy these aircrafts and fighter jets here near the Philippines and that will be a grave threat to our security."
Woody Island is part of the disputed Paracel Islands chain, some 1,000 kilometers off the Philippines' coastline.
Freedom of navigation is a principle of customary international law that, apart from the exceptions provided for in international law, ships flying the flag of any sovereign state shall not suffer interference from other states.
Under the UN Convention on the Law of the Sea, or UNCLOS, a coastal state's sovereignty extends 12 nautical miles into the ocean. This 12 nm zone is known as the "territorial sea." A coastal state also receives an "Exclusive Economic Zone," which extends 200 nautical miles from its coastline. Within its EEZ, a coastal state has the exclusive right to exploit mineral resources in the seabed, among other entitlements.
