About 50 men with machine guns came a Nigerian prisono Sept. 8, forced the prison open and released about 800 prisoners. AP Heavily armed gunmen attacked a prison in the central Nigerian city of Bauchi late on Tuesday, freeing as many as 800 inmates including suspected members of a militant Islamic sect, police said on Wednesday.

State police commissioner Danlami Yar'Adua said the gunmen killed four people including two bodyguards and set part of the prison on fire. He said everything possible was being done to track down the escaped prisoners.

"About 50 men with machine guns came to the prison site, forced the prison open and released all the prisoners," one Bauchi resident told Reuters, asking not to be named.

Residents said the attackers were believed to be members of Boko Haram, a radical Islamic sect behind an uprising which killed hundreds of people in and around the northern city of Maiduguri a year ago.

Followers of Boko Haram -- which means "Western education is sinful" in the Hausa language spoken across northern Nigeria -- want sharia (Islamic law) imposed more widely across Africa's most populous nation.

The Bauchi prison was holding members of the sect who were detained after last year's uprising.

The killing of several policemen in recent weeks, and of two traditional rulers in the past week, had already raised fears in Maiduguri that Boko Haram was making a return.

Security has been tightened in Maiduguri, with the police and army carrying out joint patrols and a dusk-to-dawn ban imposed on motorcycles, which have been used by gunmen to carry out the recent attacks.

Symbols of government authority, including police stations, prisons and schools, were among the buildings attacked at the beginning of last year's uprising. Nearly 800 people were killed, many of them shot by the security forces, in gunbattles which raged for days as the police and army fought to put down the uprising by sect members armed with home-made guns, machetes and knives.