The Philippines identified on Monday four more of its military bases that the United States will get access to, almost doubling the number included in a defense agreement that seeks to advance a decadesold alliance between them.

The expansion of the Enhanced Defense Cooperation Agreement (EDCA) underlines the Philippines' strategic importance to former colonial ruler the United States, coming at a time of growing concern over China's conduct in the South China Sea and tension over self-ruled Taiwan.

The EDCA, signed in 2014 under U.S. President Barack Obama, allows U.S. access to Philippine bases for joint training, pre-positioning of equipment and building of facilities such as runways, fuel storage and military housing, but it is not a permanent presence.