Investigators probing the Catholic cathedral bombing that killed 21 people in the Philippines' restive south said Monday a group tied to notorious Islamists Abu Sayyaf is the prime suspect.
Two explosions tore through the cathedral on the Muslim-majority island of Jolo, killing worshippers at Sunday mass and security forces in an attack claimed by the Islamic State group.
Authorities said the so-called Ajang-Ajang faction is a small band of several dozen that most likely carried out the bombing, the Philippines' worst in years, in an act of revenge.
"Last year their leader was killed. There have been persistent reports that they will retaliate," regional military spokesman Lieutenant Colonel Gerry Besana told AFP.
"Yes, we saw them in the CCTV. It was the brother of the leader who was killed," he said referring to footage from outside the cathedral. "He was seen with two other members of Ajang-Ajang."
"Not all members of Ajang-Ajang group are pro-ISIS, but all of them are Abu Sayyaf group," said Banlaoi using another acronym for IS. "It's not IS-affiliated."