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By Jeff Koinange
Lagos Bureau

LAGOS, Nigeria (CNN) -- Authorities in the northern Nigerian city of Kano confirmed at least 18 dead Sunday, after two days of clashes between police and anti-U.S. protesters. Others said hundreds may have died.

By Sunday night, city streets were quiet, but gunfire could be heard in the suburbs. Despite official accounts of the number of dead, witnesses told CNN they had seen hundreds of bodies in the streets and elsewhere.

The protests began peacefully Friday as a reaction against the U.S.-led airstrikes in Afghanistan, but turned violent Saturday.

Some of the fighting was attributed to traditional rivalries between Christians and Muslims. After the violence began, many non-Muslims fled to police stations and military barracks for safety.

Additional government troops entered Kano Sunday to help police keep the peace, after many residents ignored an overnight curfew.

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Although Saturday's violence was linked to the bombardment of Afghanistan, it followed a familiar pattern of deadly religious clashes that have rocked Nigeria over the past two years, killing thousands.

The introduction of Islamic law in some northern states triggered Muslim-Christian fighting in cities in the region.

Nigeria's population of about 120 million is split almost evenly between Muslims and Christians