MANILA, Feb 3 - The United States is open to the possibility of joint naval patrols with the Philippines in the East Vietnam Sea, a U.S. diplomat said on Wednesday, stressing it would continue to exercise "freedom of navigation" in the disputed waters.

China claims most of the East Vietnam 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 of an island claimed by China in the East Vietnam 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 Da Chu Thap (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 [East Vietnam Sea] and we will continue to do so."

The Philippine has challenged Beijing before the arbitration court in The Hague, a case Beijing has not recognised.

Foreign and defence ministers from the United States 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 East Vietnam Sea.

The United States has no East Vietnam 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.