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Suspected bomb explosion kills 9, wounds more than 20 others on Philippine passenger bus

  • In this photo taken late Tuesday, Dec. 9, 2014, and released by the Maramag Police Station of the Philippine National Police, an investigator examines a passenger bus following an explosion at Maramag township, Bukidnon province in southern Philippines. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday, Dec. 10, 2014. (AP Photo/Maramag Police Station of the Philippine National Police)

    In this photo taken late Tuesday, Dec. 9, 2014, and released by the Maramag Police Station of the Philippine National Police, an investigator examines a passenger bus following an explosion at Maramag township, Bukidnon province in southern Philippines. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday, Dec. 10, 2014. (AP Photo/Maramag Police Station of the Philippine National Police)  (The Associated Press)

  • In this photo released by the Maramag Police Station of the Philippine National Police, investigators examine the blood-splattered passenger bus Wednesday, Dec. 10, 2014 at Maramag township, Bukidnon province in southern Philippines, following an explosion late Tuesday. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday. (AP Photo/Maramag Police Station of the Philippine National Police)

    In this photo released by the Maramag Police Station of the Philippine National Police, investigators examine the blood-splattered passenger bus Wednesday, Dec. 10, 2014 at Maramag township, Bukidnon province in southern Philippines, following an explosion late Tuesday. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday. (AP Photo/Maramag Police Station of the Philippine National Police)  (The Associated Press)

  • In this photo taken late Tuesday, Dec. 9, 2014 and released by the Maramag Police Station of the Philippine National Police, an investigator examines a piece of shrapnel found from a passenger bus at Maramag township, Bukidnon province in southern Philippines, following an explosion. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday, Dec. 10,2014. (AP Photo/Maramag Police Station of the Philippine National Police)

    In this photo taken late Tuesday, Dec. 9, 2014 and released by the Maramag Police Station of the Philippine National Police, an investigator examines a piece of shrapnel found from a passenger bus at Maramag township, Bukidnon province in southern Philippines, following an explosion. The death toll from a suspected bomb explosion on the bus in the southern Philippines rose to at least 10 with more than 30 others wounded, officials said Wednesday, Dec. 10,2014. (AP Photo/Maramag Police Station of the Philippine National Police)  (The Associated Press)

Police say a suspected bomb blast has killed at least nine people and injured more than 20 others on a bus in front of a university in the southern Philippines.

Police officer Rufina Bayarcal says a powerful blast ripped through the bus Tuesday as it was traveling near the gate of Central Mindanao University in Bukidnon province's Maramag town.

Investigators are trying to determine the source of the explosion.

A 17-year-old student aboard the bus, Ralph Quilla, said by cellphone that the blast at the back of the vehicle sent shrapnel and debris flying and wounded him in the arm.

Muslim rebels and extortion gangs have been blamed for bus bombings in the south in the past.