Extra security forces have been deployed in parts of Nigeria after deadly rioting over cartoons of the prophet Muhammad spread to sub-Saharan Africa. Police are reporting 15 people were killed during anti-Christian violence on Saturday.
Residents in the northeastern Borno state spent the night under curfew, while reinforcements arrived to quell communal tensions.
More than 100 people were detained in Borno state's capital, Maiduguri, where protesters ran wild after police tried to disperse them with tear gas. They responded by looting Christian shops, burning churches and attacking Christians on the streets.
The state governor said he was shocked and disgusted.
Most of the dead are believed to have been Christians, who represent a sizeable minority in the increasingly radical Islamic north.
An expert on Islamic issues, Shehu Sani, said the cartoon issue must be closely monitored in Nigeria, or else, he warned, it could spiral out of control.
"There should be vigilance at this very sensitive and tense moment to ensure that the situation is not exploited by any individual or group," he said. "But the anger is plausible and visible in every face of Muslims throughout the country."
Compared to other parts of the world, sub-Saharan African had so far not had any violence related to the cartoons.
But last week, assembly members in another northern state, Kano, burned Danish flags and called for a boycott of Danish goods. Fearing this kind of violence, Nigerian Christian groups had already denounced the publication in Denmark and other European newspapers of cartoons depicting the prophet Muhammad as a terrorist.
In 2002, a Miss World beauty pageant competition had to be moved out of Nigeria, after a newspaper columnist said the prophet might have liked one of the contestants to be his wife, leading to violence then that killed more than 100 people.