The bus was traveling with more than 50 passengers when the powerful blast shook the rear of the vehicle from the overhead compartment, police Chief Superintendent Gil Meneses said. The force of the explosion was so strong it decapitated two of the victims, he said.
Ten people, including the bus conductor, died in the blast in Matalam township in North Cotabato province, said police spokeswoman Senior Inspector Joyce Birrey.
No one immediately claimed responsibility for the blast.
The southern Philippines is home to kidnappers, extortion gangs and a decades-old Muslim insurgency.
President Benigno Aquino III condemned the bombing and ordered police to step up security at possible terrorist targets.
Police and army units interviewed survivors and examined the twisted metal and other debris to determine the type of explosive, Meneses said. An ordnance team said it appeared to be an 81mm mortar round that was remotely detonated using cellular phones.
The driver told police three men who boarded the bus along the highway got off minutes before the blast. Their sketches were being prepared from witnesses’ descriptions, Birrey said.
Military spokesman Lt. Col. Randolph Cabangbang said authorities suspect the Al-Khobar extortion gang in the attack, saying the bus company involved in the bombing had been targeted for extortion in the past.
Al-Khobar is the most notorious of the region’s extortion gangs, and authorities say it is made up of criminals and former Muslim rebels who have been blamed for attacking businesses that refuse to pay their ransom demands. The group is on a US list of terrorist organizations.
In April last year, two homemade bombs exploded hours apart on one bus, wounding the conductor and five passengers. A bomb exploded at a Cotabato city bus terminal in February the same year, wounding two people.
Troops last year captured a suspected Al-Khobar leader, Mokasid Dilna, who allegedly trained with militants in Afghanistan and Pakistan in the 1990s. Military officials said he provided refuge to foreign militants and acted as a link with two local Muslim groups — the violent Abu Sayyaf and the larger Moro Islamic Liberation Front, which has been engaged in peace talks with the government.
Mohagher Iqbal, the chief negotiator for the Moro rebels, said his group had no involvement in Thursday’s bombing.
“We have forces there, but not along the highway,” he told The Associated Press. “We will never get involved in matters like that.”
