Nigerian forces have tightened security at a market in the northeastern city of Maiduguri following an attack late Monday by gunmen that killed as many as 30 civilians.

The military confirmed the fighting but denied any civilian deaths. It said eight militants, believed to be members of the extremist Islamic sect Boko Haram, were killed in an ensuing shoot-out, though the group said that none of their members were killed.

A Boko Haram spokesman said the attack was in revenge for market traders turning in a suspected Boko Haram member to authorities.

A trader in the market told VOA the militants attacked them with explosives and guns because market vendors helped capture one of their members. He said many innocent lives have been lost and the vendors will not assist security forces in the future. The trader said they called on the government to salvage the situation because it is civilians who are on the receiving end of the violence now.

Boko Haram, which in the Hausa language means “Western education is a sin,” has staged dozens of attacks in the country's north against military and police targets, as well as churches and mosques. Several hundred people have died in those attacks.

The group seeks to undermine state authority and to establish strict Sharia, or Islamic law, in northern Nigeria. The country is roughly divided between the largely Muslim north and the mostly Christian south.

Many argue that dialogue, and not military force, is needed to end the violence. However, Boko Haram said Tuesday that it would not enter into mediation until all of their arrested members have been released unconditionally.