At least 13 people are now reported dead and 41 injured after at bomb exploded at a busy department store in the southern Philippines city of General Santos.
Two other bombs reportedly went off at the Radio Mindanao Network office a few minutes later, and another explosion was reported two hours afterward elsewhere in the city.
Police said they received a call claiming 18 bombs had been planted around the largely Christian city of 800,000 people in the predominantly Muslim south. Police arrested three Filipinos in city suspected of links the al Qaeda network and confiscated a tonne of explosives from them in January.
Later a man who said he represented a local Muslim guerrilla group claimed responsibility for the bomb attacks.
The man, who identified himself as Abu Muslim al Ghazi with links to the Abu Sayyaf guerrilla group operating in the country's south, called local RMN radio just after the explosions, station manager Elmer Ubaldo said.
The Abu Sayyaf has been holding a US missionary couple hostage for almost 11 months on Basilan island, 350 km (about 215 miles) west of General Santos.
Senior Superintendent Bartolome Baluyot, police chief for the central Mindanao region, said early reports indicated that an unknown number of home-made bombs had been planted inside and outside the Gensan Fitmart department store near the central city plaza.
Councillor Eduardo Leyson said one exploded in an empty motorised tricycle in front of the shop shortly after 3 p.m. (8 a.m. Irish time), and there were unconfirmed reports of another nearly simultaneous blast.
At least two unexploded bombs were discovered under a lorry parked in front of the shop - they were being dealt with by the police bomb squad.
The injured were taken to hospitals in the city, a little over 620 miles southeast of Manila.
AP