Subi reef, located in the disputed Spratly Islands in the South China Sea, is shown in this handout CSIS Asia Maritime Transparency Initiative...

WASHINGTON (Reuters) – The U.S. Navy will likely carry out another patrol within 12 nautical miles of artificial islands in the South China Sea before the end of the year, a U.S. Navy official said on Friday.

The USS Lassen, a guided missile destroyer, last month sailed close to one of China’s man-made islands in the Spratly Islands archipelago to underscore its rights under international law, drawing an angry rebuke from Beijing.

A U.S. defense official said this month the Navy planned two or more patrols a quarter in the region as part of its plan to regularly exercise its rights under international law and remind China and others about its view.

The U.S. Navy official said the next patrol in the Spratly Islands archipelago would likely take place in December.

Two U.S. B-52 bombers also flew near the artificial Chinese islands last week, in advance of President Barack Obama’s visit to the region this week to attend Asia-Pacific summits.

Obama on Friday said the disputed region would be a major focus of summit meetings among world leaders this weekend in the Malaysian capital of Kuala Lumpur.

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

On Thursday, Obama demanded China halt land reclamation work that is turning seven reefs into artificial islands. China is building airfields and other facilities on some of them.

In a report published on the Chinese defense ministry’s website on Thursday, China’s top admiral, Wu Shengli, said his forces have shown “enormous restraint” in the face of U.S. provocations in the South China Sea, while warning they stand ready to respond to repeated breaches of Chinese sovereignty.

Earlier this month, Senator John McCain, the Republican head of the Senate Armed Services Committee called on the Pentagon to clarify publicly the legal intent of last month’s patrol.

U.S. officials said the Navy avoided military drills that could have exacerbated tensions with Beijing during the Lassen’s Oct. 27 patrol in the Spratly Islands, an approach experts said could reinforce rather than challenge China’s sovereignty claims.