U.S. Defense Secretary Ashton B. Carter at an International Institute for Strategic Studies conference in Singapore, where he called for a halt to South China Sea reclamation projects. (Maye-E Wong/Associated Press)

U.S. Defense Secretary Ashton B. Carter said Sunday that he will urge Vietnam to give up its reclamation projects in the South China Sea, making a direct plea after earlier calling for all countries in the Asia-Pacific region to halt the construction of artificial islands.

China’s rapidly expanding building projects have raised tensions and caused concerns among the United States and its regional partners.

Speaking to reporters during a stop at a Vietnamese navy base, Carter said that all the claimants in the South China Sea must halt their reclamation efforts and any further militarization of the sites. Those would include Vietnam, Malaysia, the Philippines and Taiwan, but their projects are dwarfed by China’s building program on reefs and atolls, now totaling more than 2,000 acres.

The United States and others are concerned that China will use the artificial islands as military bases and to assert control over South China Sea navigation.

Carter’s comments came in the wake of disclosures that China had placed two motorized artillery vehicles on one of its reclamation sites. Officials have said that the artillery has been moved.

This was Carter’s first trip to Vietnam as defense secretary, and the first time a U.S. defense secretary had visited a Vietnamese navy base or toured a military ship.

Carter said he planned to talk with officials in Vietnam about ongoing U.S. efforts to provide maritime defensive weapons to the country.

In October, the United States partially lifted its ban on weapons sales to Vietnam to boost the country’s ability to defend itself in the South China Sea. Only the sale of lethal maritime security and surveillance capabilities are allowed on a case-by-case basis, including boats and air assets. But no weapons have flowed to Vietnam to date.

Sen. John McCain (R-Ariz.) said Saturday that the United States should gradually lift the Vietnam weapons ban considering the country’s issues with China.

Both McCain and Carter attended an international security conference over the weekend in Singapore, where Carter first called to suspend reclamation.

McCain, chairman of the Senate Armed Services Committee, said the United States should provide additional defensive weapons that could be used in case of a conflict with China, but should continue its ban on weapons that could be used for crowd control or potentially to commit human rights abuses.