MANILA, Philippines -- Police in Manila, Philippines, believe an al Qaeda-linked group could be responsible for the bombing of a passenger bus that killed four people.
The powerful explosion happened Tuesday in the Philippine capital's financial district. Fourteen others were injured.
Authorities suspect the explosion was caused by a homemade bomb.
The explosion happened at around 2:00 p.m. as the passenger bus traveled the main highway near a major business center.
Metro Manila police chief Nicanor Bartolome said an improvised explosive device was placed under a passenger seat somewhere in the middle of the bus.
Authorities are still investigating, but they are not discounting the fact that this incident could be part of a destabilization plot against President Benigno Aquino III's administration.
Police believe the attack could be the work of terrorists. The Filipino government has been fighting a decades-long battle with Islamic separatists in the southern part of the island nation. Rebels have targeted buses in the past.
But law enforcement officials say it could also be an attempt to thwart a government investigation into criminal activity in the capital. Officials are investigating high-profile carjackings and possible collusion between the criminals and government officials.
Meanwhile, in the midst of all the violence, the national capital region including metro Manila is on full alert.