MANILA — Militants detonated a car bomb at a military checkpoint on Tuesday in the southern Philippine island of Basilan, killing at least 10 people in a brazen attack that underscored the continuing insurgent threat in the southern part of the country.

The attack happened as troops flagged down a van at a roadblock heading into Lamitan City. When the driver failed to answer questions, he apparently detonated the explosive, the military said.

The blast instantly killed a soldier, three pro-government militiamen and several civilians, the military said. Nine others, including five soldiers, were injured.

Lt. Col. Mon Aldomovar, commander of the Third Scout Ranger Battalion in the area, said he suspected that the militant group Abu Sayyaf was behind the bombing.