MANILA (Reuters) - The Philippines on Monday foiled a bid to plant car-bombs at its main airport and a nearby shopping mall, authorities said.

The motive for the bomb plot was not immediately clear but in the past such attacks in Manila, the capital, and other parts of the largely Christian Philippines have been blamed on al Qaeda-linked Islamist militants from the Abu Sayyaf group.

Agents of the National Bureau of Investigation (NBI) found improvised explosive devices in a parking area at the Ninoy Aquino International Airport.

Three men were arrested but no details were released pending investigation. Airport authorities went on full alert.

NBI director Virgilio Mendez said three suspects had been taken in to custody but he declined to give more details.

Another NBI official, who declined to be identified because he is not authorized to speak to reporters, said the suspects had been under surveillance for a month.

“They were assembling the improvised bombs inside their vehicles at the airport parking lot. There may be other targets,” the official said, adding that up to eight bombs and a pistol were confiscated from the suspects.