The United States is open to the possibility of joint naval patrols with the Philippines in the South China Sea, a U.S. diplomat said Wednesday, stressing it would continue to exercise “freedom of navigation” in the disputed waters.

China claims most of the South China Sea, through which more than $5 trillion of world trade is shipped every year. Vietnam, Malaysia, Brunei, the Philippines and Taiwan have rival claims.

A U.S. Navy destroyer sailed within 12 nautical miles (22 km) of an island claimed by China in the South China Sea on Saturday to counter efforts to limit freedom of navigation, the Pentagon said, prompting an angry reaction from Beijing.

Manila has asked the U.S. to patrol the area together after China began test flights from Fiery Cross Reef, one of three artificial islands where Beijing has built airfields.

“We do discuss that principle (joint patrols) with the Philippines and so I am not discarding that possibility,” U.S. Ambassador to the Philippines Philip Goldberg told reporters.

“But we are not going to make announcements about that beforehand because it is our view that we have every right under international law to exercise freedom of navigation in the South China Sea and we will continue to do so.”

The Philippines has challenged Beijing before the arbitration court in The Hague, a case Beijing has not recognized.

Foreign and defense ministers from the U.S. and the Philippines met in Washington last month for the second time in more than three years to discuss trade and security, focusing on the South China Sea.

The United States has no South China Sea claim and says it takes no sides, though it has been highly critical of China’s assertiveness.

It carried out a navy patrol near areas claimed by China, Taiwan, Vietnam and the Philippines in October.