A bomb attached to a motorcycle blew up outside a southern Philippines (search) open-air gymnasium packed for a basketball game Sunday, killing 11 people and injuring at least 68 others, officials said.

No one has claimed responsibility for the blast. But investigators believe the bomb was intended for Mayor Vivencio Bataga (search), a tough-talking former army officer who has survived three attempts on his life.

Bataga was talking to someone outside the gym when the explosion occurred. His teeth were knocked out and he suffered shrapnel injuries in the ribs, but he was reported in stable condition.

Bataga told reporters from his hospital bed in nearby Cotabato (search) city that he believed the attack was aimed at him.

Bataga blamed political rivals or drug syndicates for a September bombing in front of a church where he was attending Mass with his family. One of his bodyguards was slightly wounded in that blast.

Assailants earlier fired a rocket-propelled grenade that missed Bataga's vehicle and a bomb exploded while he was in a public market in April.

Aside from fighting drug dealers in Parang, a predominantly Muslim coastal town 515 miles south of Manila, Bataga also is a vocal critic of Muslim guerrillas active in the area.

But Eid Kabalu, spokesman of the Muslim separatist Moro Islamic Liberation Front (search), condemned Sunday's attack and said his group will help authorities track down the perpetrators.

Authorities said the bomb was planted on a motorcycle parked five yards from the gymnasium.

Police officer Sharifa Irijani said many of the injured were hit by shrapnel, while others were hurt in a stampede following the blast. Irijani said she counted at least 10 bodies and scores of injured, including a policewoman's 11-month-old daughter, when she arrived at the scene.

Chief Inspector Oscar Nantes, the head of police in Parang town, told Manila radio station DZRH that the casualty toll was gathered from nearby hospitals.

The southern Philippines has the largest number of illegal weapons in the country, and gunrunning syndicates readily sell weapons to rebel and criminal groups there.