
Troops and police reinforcements have been deployed to restore order in the northeastern city of Maiduguri, where 15 Christian churches were burned, said Nigerian police spokesman Haz Iwendi.
Chima Ezeoke, a Maiduguri resident, said the protesters attacked and looted shops in the city owned by minority Christians, most of them with origins in the country's south.
"Most of the dead were Christians beaten to death on the streets by the rioters," Ezeoke said.
Nigeria, Africa's most populous country of more than 130 million people, is roughly divided between a predominantly Muslim north and a mainly Christian south.
The cartoons, which first appeared in a Danish newspaper in September, have set off sometimes violent protests around the world. One caricature shows Muhammad wearing a bomb-shaped turban with an ignited detonator string.
Islam widely holds that representations of Muhammad are banned for fear they could lead to idolatry.