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

Three people were arrested after a bomb was found in a van parked at Manila's international airport, but there was no ongoing safety threat for travelers, they said on Monday.

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 Philippines have been blamed on 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.

A utility vehicle containing an "improvised explosive device" was found at the airport's terminal three car park about 1:45 a.m. (1745 GMT) Monday, said a short report released by the National Bureau of Investigation.

In brief comments to reporters, NBI director Virgilio Mendez refused to give many details about the incident, saying "there is an ongoing follow-up operation".

Other authorities involved in the investigation also declined to comment.

But the terminal, which serves domestic flights as well as international airlines, operated as normal on Monday and the Manila International Airport Authority said there were no continuing threats.

"(The authority) assures the public that (terminal three) and all other terminals remain safe and airport security personnel continue to stay vigilant in their respective areas," it said in a statement.

The initial National Bureau of Investigation said four suspects were arrested, but Mendez later said only three men were in custody.