- The explosion struck a market in northeast Nigeria's Borno state
- Although no one has claimed responsibility for the attack, Boko Haram is the prime suspect
- The militant group has mounted a campaign of bombings, kidnappings and deadly raids in recent years
The hospital source and the vigilante, Abbagana Saleh, both are based in the town of Biu, about 50 kilometers (32 miles) from the blast scene. Victims from the explosion were taken to Biu General Hospital.
The blast occurred early Tuesday afternoon at a weekly market in the town of Sabon Gari.
Although no one has claimed responsibility for the attack, Boko Haram is the prime suspect. The militant group has been carrying out ambushes along the highway that intersects Sabon Gari, and links it with the larger towns of Biu as well as the state capital Maiduguri.
On Sunday, Boko Haram killed four people and abducted five others in an ambush on two vehicles in Nwajurko village, near Sabon Gari.
The group has mounted a campaign of bombings, kidnappings and deadly raids in recent years. It says it wants stricter enforcement of Sharia law across Nigeria, which is split between a majority Muslim north and a mostly Christian south.