Manila, April 23 -- Surveillance of Philippine vessels en route to the West Philippine Sea may be part of a wider and coordinated espionage operation tied to Chinese maritime forces, the National Bureau of Investigation (NBI) told a Senate panel on Wednesday.

Senate Majority Leader Francis Tolentino, who chairs the Special Committee on Maritime and Admiralty Zones, raised the alarm over intelligence reports that Chinese vessels were aware of Philippine resupply missions before ships even departed Palawan - suggesting possible coordination with foreign nationals recently arrested for suspected spying.

"There is a possibility, Mr. Chair, kasi yung Palawan 5 po ang sinu-surveillance niyan (ay) yung mga vessels po natin na papuntang (becaus...