Sri Lanka, March 28 -- Philippine authorities announced the arrests of six Chinese nationals and a Filipino suspected of spying on U.S. and Philippine navy vessels at the entrance of the strategically located Subic Bay.

The arrests of the Chinese suspects, who officials said were posing as fishermen, brought to 12 the number of Chinese citizens taken into custody in the Philippines this year for alleged espionage. The cases have unfolded against the backdrop of heightened tensions between Manila and Beijing in the contested South China Sea.

The seven suspects were arrested on March 19 after Philippine military intelligence alerted the National Bureau of Investigation about "foreign nationals suspected of carrying out covert intelligence...