Witnesses told reporters that protesters turned on the Christian minority in the northern city of Maiduguri on Saturday, burning shops and churches, after police dispersed a rally called to condemn European newspapers that printed the caricatures.
A police spokesman, Deputy Commissioner Haz Iwendi, told reporters that army troops and police reinforcements had been deployed to the city and that a curfew had been imposed to bring about a return to order.
"We've arrested 115 people. Some 15 persons were killed by rioters, and 11 churches burnt," he said.
The victims were the first to die in Nigeria as anger over the drawings of Islam's prophet mounts among its 60 million Muslims, roughly half the population.
Mohammed Auwal, a civil servant, told reporters by telephone: "When the protesters gathered for the protest at Ramat square they were ordered by a police detachment to disperse but the crowd insisted on holding the protest."
"The policemen then fired canisters of teargas to disperse the crowd.
"We've arrested 115 people. Some 15 persons were killed by rioters, and 11 churches burnt"
Police Deputy Commissioner
"When news went into town about what happened at the square, a mob attacked motor spare-parts shops of Christian Igbo traders at Monday market in the city, looting and burning them," Auwalu said.
A local reporter, Abdullahi Bego, told reporters from the scene that at least 20 shops had been looted and vandalised and churches had been burned to the ground.
"There are a lot of anti-riot police squad all over the city and their presence has helped quell the rampage," Bego said. Ibrahim Bukar, a student, said: "I have been indoors since the riots broke out, but a friend told me he saw two dead bodies at the scene of the looting."
In recent weeks there have been protests around the world -some peaceful, some violent - by Muslims angry over the publication in European newspapers of cartoons satirising Islam's holiest figure, Prophet Muhammad.
In a radio broadcast following the violence, Ali Modu Sheriff, the local governor, said: "The Borno State government is shocked and disgusted."
Sheriff, a Muslim like the vast majority of Borno State residents, said that while he sympathised with the feelings of Muslims offended by the cartoons, Nigerian Christians should in no way be blamed for them.
He promised that the perpetrators of the violence would be punished.
In Abuja, Frank Nweke, the Nigerian information minister, called on religious leaders to rein in their angry followers.
Call for calm
"The federal government, while it does not begrudge any group the right to defend their faith and religion, also believes that certain actions - such as burning of churches - are not the best way," he told reporters.
Northern Nigeria is overwhelmingly Muslim, but major cities have significant Christian minorities, mainly members of the Igbo ethnic group who operate successful small businesses, trading especially in car parts and alcohol.
Religious tensions often turn
violent in Nigeria
Since 1999 a dozen northern states, including Borno, have attempted to reintroduce Islamic Sharia law, exacerbating latent tensions between the communities and triggering several bloody riots.
Sometimes external factors such as the cartoon controversy trigger the fighting. In September 2001 news of the attack by al-Qaida hijackers on New York and Washington rekindled unrest in Jos which killed 915 people.
And in 2002 an attempt to stage the Miss World beauty contest in Nigeria offended conservative Muslims and led to a riot which left 220 dead.