MANILA (AFP) - Philippine police have recovered a powerful explosive device inside an Indian businessman's car, an official said Thursday.

A car repair shop near Manila alerted police after a mechanic found the device on Wednesday inside the vehicle's engine compartment, which the owner and two compatriots had driven there for repairs, said Chief Superintendent Benito Estipona.

"It appears they did not know about the bomb. The theory is they might have been the target," Mr Estipona, the regional police chief, told reporters.

He described the bomb as made from military-grade C-4 explosives rigged to a mobile phone as a trigger device.

Mr Estipona said the three Indian men are being questioned by police in Alaminos, three hours' drive south of Manila, where the explosive device was found.

He declined to elaborate and gave no other details about the men.

Violence related to business or political rivalries is common in the Philippines, where there is an active black market for weapons, such as guns and explosives.