Witnesses in Nigeria say fighting between soldiers and Islamist insurgents in a market in the country's northeast has left at least 20 people dead.

Residents and medical personnel in the city of Maiduguri say the dead, who they identify as mostly civilians, were killed when the fighting erupted Monday in the popular Baga market.

Military officials confirm the fighting but deny any civilian deaths. They say security forces killed eight assailants and safely detonated several bombs planted by the attackers.

The insurgents are believed to be from the group Boko Haram, which has staged dozens of attacks across northern Nigeria over the past year. Several hundred people have been killed in those attacks.

The group is seeking to establish strict Sharia law in the northern part of Nigeria. The country is roughly divided between the largely Muslim north and the mostly Christian south.