A huge explosion rocked the southern Philippine city of General Santos on Sunday, killing 13 people and injuring at least 60 at a public market.
Shoppers and merchants fled the market in panic after the explosion and police cordoned off the area.
Three people died at the scene and 10 in three different hospitals, said Chief Superintendent Antonio Billiones, the region's police chief.
"We are still investigating to determine the type and make of the explosive device used in the attack," he told reporters.
Police noted recent reports of threats by Muslim rebels from the Abu Sayyaf, a homegrown group linked to the regional militant network Jemaah Islamiah (JI). But the mayor of General Santos said the blast could have been caused by feuding merchants.
Billiones said police has been getting intelligence reports, as early as September, on alleged plans by the Abu Sayyaf to bomb the city.
Police said the last major bomb attack in the city killed 15 and injured dozens when an improvised explosive device ripped through a crowded shopping mall in April last year.
The attack was blamed on Abu Sayyaf rebels, but security officials say the regional terror network Jemaah Islamiah planned, financed and directed the attack.