At least 10 people were killed when two suicide bombers set off an explosion outside a crowded market in Maiduguri.
A security officer told AP he counted as many as 10 corpses, but the death toll could be much higher at the latest attack to hit the biggest city in northeastern Nigeria.
Witnesses said the one suicide bomber exploded near a tricycle taxi.
"I saw many dead bodies lying on the ground, many dead, and several others badly injured," said fish seller Idi Idrisa.
No-one has claimed responsibility for the attack, but it bears the hallmarks of the Boko Haram Islamic extremist group.
Boko Haram has also attacked villages in Cameroon and Niger, as Nigeria's neighbours are forming a multinational force to confront the spreading Islamic uprising.
Boko Haram fighters are gathering at their headquarters in the northeastern town of Gwoza, in a possible showdown with multinational forces, according to witnesses who escaped from the town.
An intelligence officer said they were aware of the movement but that the military is acting with care as many civilians are still trapped in the town and Boko Haram is booby trapping the area with land mines placed around it.
About 12,000 people have died in the six-year violent insurgency which has focused in north-eastern Nigeria.