Defense Secretary Ash Carter strongly defended U.S. flights over artificial islands that Beijing is building in the South China Sea Wednesday, but did not give any indication of what the U.S. was willing to do to stop the buildup.

"There should be no mistake in this, the United States will fly, sail and operate wherever international law allows,” Carter said, responding to Chinese complaints about U.S. military flights over the projects.

Carter’s comments come in the wake of a formal Chinese protest over last week's flight of a U.S. Navy P-8A Poseidon surveillance aircraft over Fiery Cross Reef. Carter’s message signals a sharp start to his 11-day trip in Asia, where he will make stops in Singapore, Vietnam and India.

However, Carter did little to clarify what the U.S. is willing to do to get China to halt the island construction.

One senior U.S. official told The Associated Press there are discussions about conducting more military flights and patrols in the South China Sea near the projects. Officials are also looking at ways to adjust the military exercises in the region to increase U.S. presence there if needed.

One possibility would be for U.S. ships to travel within 12 miles of the artificial islands, to further point out that they are not sovereign Chinese land.

The Navy routinely conducts surveillance and other aircraft flights in the Asia-Pacific region, but China's escalating land reclamation projects have raised concerns about the country's military intentions. China further inflamed tensions Tuesday by issuing a report that laid out Beijing's more assertive national defense posture.

China insists the building is within its rights and has no intention of stopping.

Carter, who spoke during a leadership handover ceremony Wednesday in Hawaii, called for an “immediate and lasting halt” to all land reclamation projects by all Pacific nations.

China’s building far outstrips any other nation's efforts, though Vietnam has also done some land reclamation projects.

While the U.S. has many disagreements with China, the two nations have worked to improve relations in recent years through increased diplomatic and military contacts.

The Pentagon said in a recent report that the construction — estimated at more than 2,000 acres — could be used for military airstrips, naval ports or to host surveillance systems. U.S. officials are concerned that China's land reclamation projects may be a prelude to enforcing a possible air defense identification zone over the South China Sea, similar to one it declared over disputed Japanese-held islands in the East China Sea in 2013.

The U.S. official said there are concerns that China is working to build a perimeter around the South China Sea so it potentially can claim the entire region as its own economic zone, with rights to all the natural resources there.

The Associated Press contributed to this report.