HAIPHONG, Vietnam -- US Defense Secretary Ash Carter said Sunday he will urge Vietnamese officials to give up their 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 has 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 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, which now totals more than 2,000 acres.

China is vigorously defending the projects in the face of persistent criticism from US leaders, who say that the building programs will not provide Beijing any additional sovereign land. The US and others are concerned that China will use the artificial islands as military bases and to assert control over navigation in the South China Sea.

Carter also toured a Coast Guard ship a day before his scheduled meetings with Vietnamese leaders. Other topics expected to come up are maritime weapons sales

Carters' comments come in the wake of disclosures that China had placed two motorized artillery vehicles on one of its reclamation sites. Officials have said the artillery has been moved.

This is Carter's first trip to Vietnam as defense secretary, and the first time a US defense secretary has visited a Vietnamese Navy base or toured a military ship.

Two years ago, US Defense Secretary Leon Panetta visited the former US air and naval base at Cam Ranh Bay in Vietnam and went on board the USNS Richard E. Byrd, a cargo ship operated by the US Navy's Military Sealift Command.

Carter said he planned to talk with Vietnamese officials about ongoing efforts by the US to provide maritime defensive weapons to the country.

Last October the US 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 based on an evaluation of Vietnam's needs. But to date no weapons have flowed to Vietnam.

US Sen. John McCain said Saturday that the U.S. should gradually lift the weapons ban on Vietnam, amid heightened tensions with China over the reclamation projects.

China, Vietnam and other nations have conflicting claims over portions of the South China Sea. Both McCain and Carter attended an international security conference over the weekend in Singapore, where Carter urged the halt to reclamation projects by all in the region.

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

Carter said the US will continue to discuss changes to the arms ban. He said the US has some latitude to provide maritime weapons, including ships.(AP)