The Kano state government played down the violence, saying it couldn't confirm a religious basis to the fighting. Spokesman Ibrahim Gwawargwa said police had confirmed four people killed and 30 rioters arrested. It would impose a 7:00 p.m. to 7:00 a.m. curfew, he added. Gwawargwa blamed the rioting on ``hoodlums'' who looted shops owned by both Muslims and Christians. ``We have not found any religious aspect to this,'' he said. Yet witnesses told of Christian and Muslim rioters yelling religious slogans as they attacked bystanders believed to be of another faiths. On Galadima Road, a main thoroughfare in Kano, a mob chanted ``Allahu akbar'' - or God is Great - as they burned down buildings, including the offices of several Nigerian newspapers, said Nathaniel Inku, a journalist with the Vanguard newspaper. A group of high school students on their way to take their university-entrance exams clashed with youths who shouted religious Muslim slogans, two witnesses said, speaking on condition of anonymity. Some residents took shelter in police stations while many were holed up inside their homes. Local reporters said several churches and mosques had been at least partially burned by mobs. Speaking in a telephone interview, Kano police commissioner Yakubu Bello Uba said he had ordered his officers to shoot protesters and combatants on sight. On Friday, police fired tear gas to break up a protest by hundreds of Muslim youths denouncing U.S.-led airstrikes on Afghanistan. Several people were injured and three vehicles - including a police truck - were burned. Chanting ``Americans are infidels'' and ``Leave Bin Laden alone,'' the marchers gathered after Friday afternoon Muslim prayers. The U.S. began its military campaign against Afghanistan on Oct. 7 after the ruling Taliban refused to hand over bin Laden and his lieutenants to the United States. Bin Laden is the prime suspect in the Sept. 11 attacks on New York and Washington. Protesters said the rally had been organized by a group called Muslim Revolutionaries, believed to be an offshoot of a fundamentalist movement led by Sheikh Ibrahim El-Zak Zaky, a well-known politician and cleric who was jailed by the military regime in the 1990s for advocating making Nigeria an Islamic state. Nigeria, with 120 million people, is divided into an overwhelmingly Muslim north and a largely Christian south. Religious tensions have increased since a dozen northern states, including Kano, began imposing Islamic law, or Shariah, last year. Islamic courts in these states have ordered the hands of thieves amputated, and several women and girls have been publicly flogged for alleged sexual indiscretions. In September, at least 165 people were killed in the city of Jos in religious fighting.