Philippine police arrested Wednesday three more suspects in the bombings in the southern Philippine city of General Santos that left 15 people dead.
Police said they are also investigating a possible link between the bombings and Osama bin Laden's terrorist network. So far, five people, all suspected of being Muslim militants, have been arrested in connection with the Sunday bombings.
Regional police chief Colonel Bartolome Baluyot said four kilos of bomb-making materials were found in the pre-dawn raid in General Santos that netted the three suspects. He said police hoped to make more arrests soon.
The first two men arrested have been charged with multiple murder and illegal possession of explosives. Colonel Baluyot said police were preparing the same charges for those arrested Wednesday.
The Abu Sayyaf, a militant Islamic separatist group operating in the southern Philippines, has claimed responsibility for the bombings, but officials are still investigating. Washington has linked the group to al-Qaida.
Two other Muslim separatist groups operate in the southern Philippines, although one of them, the Moro National Liberation Front, signed a peace accord with the government in 1996, and the other, the Moro Islamic Liberation Front, agreed to a cease-fire last year.
By far the most violent of all the Islamic separatist groups, the Abu Sayyaf have earned millions of dollars running a kidnap-for-ransom business involving the abductions of dozens of foreigners and locals during the last two years.
The United States sent Special Forces to the Philippines in February to help train the Philippine army fight terrorism. Around 1000 troops are currently conducting counter-terrorism exercises on the Abu Sayyaf stronghold of Basilan island.
The Abu Sayyaf is still holding hostage an American missionary couple and a Philippine nurse for nearly 11 months now.