Four men have been arrested after allegedly attempting to detonate a bomb at Manila's Ninoy Aquino International Airport on Monday, according to reports by state media in the Philippines. 

The suspects, who had been under surveillance for more than a month, were arrested while assembling an explosive device in a white truck parked outside one of the terminals, according to officials. 

Acting on a tip, counter-terrorism agents from the National Bureau of Investigation caught the suspects, who were also allegedly targeting a nearby shopping mall, state media said. 

Investigators are trying to establish which group was behind the bombing attempt, but militant groups with links to al-Qaeda have been fighting to create a Muslim homeland in the south of the largely Christian country.