President Rodrigo Duterte has the constitutional duty to use all legal means, including the filing of another case against China, for its threat to use force if the Philippines would insist on the arbitral ruling and extract oil in South China Sea, Supreme Court Senior Associate Justice Antonio Carpio said.

“China’s threat of war against the Philippines over the West Philippine Sea (South China Sea) reveals the aggressive design of China against the Philippines,” said Carpio,  one of the country’s leading maritime legal experts and a member of the Philippine legal team to the Permanent Court of Arbitration (PCA) in The Hague, Netherlands.

“No less than Chinese President Xi Jinping has delivered the threat personally to Philippine President Rodrigo Duterte,” he said.

Duterte disclosed on Friday before a gathering of the members of the Philippine Coast Guard in Davao City that Xi warned him that if he would insist on the PCA award on the Philippines and pursue with the oil drilling in the disputed waters, China would be forced to go to war with Manila.

In the July 2016 ruling, the PCA decided that the Philippines has sovereign rights within its 200-nautical miles exclusive economic zone (EEZ), invalidating China’s “historic claim” over the almost entire South China Sea.

“In the face of China’s open threat of war to seize Philippine EEZ in the West Philippine Sea, an area larger than the total land area of the Philippines, the President cannot simply do nothing, or worse acquiesce to China’s action, for inaction is the opposite of protecting Philippine EEZ,” Carpio said.

“Under international law, acquiescence is the inaction of a state in the face of threat to its rights under circumstances calling for objection to the threat to its rights. Acquiescence means the Philippines will lose forever its EEZ in the West Philippine Sea to China,” he said.

Carpio said this “extremely troubling development” calls for all Filipinos to unite to defend the South China Sea in accordance with the Constitution, international law and UN Convention on the law of the Sea or UNCLOS.

“The threat of China to go to war against the Philippines if the Philippines extracts oil and gas in the Reed Bank, or in any area within Philippine EEZ in the West Philippine Sea, is a gross violation of the United Nations Charter, United Nations Convention on the Law of the Sea, and the Treaty of Amity and Cooperation in Southeast Asia to which China and the Philippines are parties,” Carpio said.

Reed Bank is an offshore area internationally recognized as part of the Philippines’ EEZ.

Carpio reminded China that the UN Charter outlaws the use or threat of force to settle disputes between states.

He also said that China’s blatant threat of war against the Philippines demands that it strengthens its defenses and alliances, particularly with long-time treaty ally, the United States.

The Philippines has an existing mutual defense treaty with the US.

“The United Nations Charter recognizes the right of states to mutual self-defense against armed aggression. The Philippines can ally with the United States because the United States does not claim the West Philippine Sea or any Philippine territory,” Carpio said.

China could not be an ally of the Philippines because it wants to “grab for itself” the entire South China Sea, including the Spratly Islands, which Manila has also been claiming, he said.

“Among all the countries in the world, only China has threatened the Philippines with war over Philippine EEZ in the West Philippines Sea,” Carpio said.

He said other fellow Southeast Asian claimant countries, such as Vietnam, Malaysia and Brunei, recognize the Philippine EEZ. DMS