The bomb exploded in a commercial area of Jolo
At least six people have been killed and many others wounded when a powerful bomb exploded on the island of Jolo in the southern Philippines.
Military officials said several of the wounded were in a critical condition and the death toll could rise.
Police said they had also defused another bomb near the Mount Carmel Cathedral in Jolo.
This latest attack follows a bomb blast outside a cathedral in the southern Mindanao province of Cotabato.
That explosion, on Sunday, killed five people and wounded 55.
The French news agency AFP has reported another bomb blast in Iligan, also in the south. The homemade bomb left in a parked car wounded seven people including two soldiers, AFP said.
The Jolo bomb was hidden on a motorbike and exploded outside a hardware store; the store owner was one of those killed.
"Many of the wounded are in critical condition so there is a possibility that there will be more than two deaths," said Navy spokesman Lieutenant Colonel Edgard Arevalo.
The military is still investigating who might behind the Jolo blasts.
Jolo is the base for the Abu Sayyaf militant group. Once linked to regional Islamist networks, the gang has recently become better known for criminal brutality and high-profile kidnappings.
The group is thought to be holding a staff member of the International Committee of the Red Cross, Eugenio Vagni, who is aged 62 and in poor health.
The authorities have suspended school classes in Jolo for fear of more attacks.
The military has blamed another group, the Moro Islamic Liberation Front, for the attack in Cotabato on Sunday.
One of its leaders, Mohaqher Iqbal, has denied any involvement in the attack.