At least 12 people have been killed in the Nigerian city of Kaduna after protests against next month's Miss World beauty competition descended into bloody violence.

Business is paralysed, everybody is staying at home

Shehu Sani, civil rights activist

Many more are also believed to have died, after thousands of Muslim youths rampaged through the suburbs of the city, erecting barricades of burning tyres, setting fire to buildings, and attacking churches.

The authorities in the northern city have declared a curfew with immediate effect.

Protests started after the newspaper ThisDay published an article which said that the Prophet Mohammed would probably have chosen to marry one of the contestants if he had witnessed the beauty pageant, which Nigeria is hosting next month.

Kaduna is one of Nigeria's most volatile cities, and has been largely segregated into Christian and Muslim areas since clashes two years ago, in which more than 2,000 people died.

Text message

On Wednesday hundreds of people chanting "Allahu Akbar" (God is great) attacked the Kaduna office of the Lagos-based newspaper, which has retracted the article and published two separate apologies.

Civil rights activist Shehu Sani told the French news agency, AFP that the city had descended into "pandemonium" on Thursday, with the streets littered with burning tyres.

"Schools and public offices are shut. Business is paralysed, everybody is staying at home and the security forces are trying to avoid contact with the demonstrators," he said.

The BBC's Yusuf Sarki Muhammad says that local mosques had been calling for action against the paper and said that some people were first alerted to the article by text messages being sent to their mobile phones.

Death by stoning

The government has issued a statement, appealing for calm and assuring Muslims that those responsible for the ThisDay article would be brought to book, for exceeding "the bounds of responsible journalism."

Witnesses told Reuters news agency that the rioters have vowed to attack ThisDay offices all over the north, where Sharia law has been introduced.

Nigeria is hosting the Miss World contests after Miss Nigeria won last year

The Miss World pageant is taking place over several weeks in Nigeria, but only in the southern, largely Christian and Animist, part of the country.

Muslim groups say the contest is un-Islamic and are also upset that it began during the holy month of Ramadan.

The contest had also been threatened by a large-scale boycott by beauty queens protesting against a Sharia court's sentence of death by stoning against Amina Lawal, a woman convicted of adultery.

The Nigerian Government has moved to calm fears by promising it will not allow any Nigerian to be stoned to death and about 90 Miss World contestants have arrived in Nigeria, ahead of the final contest in the capital, Abuja, on 7 December.