MANILA, Philippines: The Philippines has granted the United States four more locations to open military bases, U.S. Defense Secretary Lloyd Austin and Philippines' Defense Secretary Carlito Galvez said during a joint news conference at the Philippine military headquarters in Manila.

The move comes amid mounting concern over China's increasing assertiveness in the disputed South China Sea, along with tension over self-ruled Taiwan.

"Our alliance makes both of our democracies more secure and helps uphold a free and open Indo-Pacific," said Austin, who is in the Philippines.

"We discussed concrete actions to address destabilizing activities in the waters surrounding the Philippines, including the West Philippine Sea, and we remain committed to strengthening our mutual capacities to resist armed attack," Austin said.

China said greater U.S. access to Philippine military bases undermined regional stability and raised tensions.

"This is an act that escalates tensions in the region and endangers regional peace and stability," China's foreign ministry spokesperson Mao Ning said.

"Regional countries should remain vigilant about this and avoid being used by the U.S."

Austin and Galvez did not specify the sites that would be opened to U.S. access. The former Philippine military chief had said the United States has asked for access to bases on the main northern island of Luzon, the closest area of the Philippines to Taiwan, and on Palawan in the southwest, near the disputed Spratly Islands in the South China Sea.

Before meeting his counterpart, Austin met Philippine President Ferdinand Marcos and assured him of U.S. support.

"We stand ready to help you in any way we can," Austin said.