Surprise raids were conducted on February 18 and 19 at the Coimbatore Central Jail by the prison authorities following intelligence reports about the prisoners planning a jail-break or attacking the jail staff, the sources said.

The raiding staff recovered knives, brass rods, wires, electronic switches, PVC pipes, leather straps and medical syringes, which the sources claimed were to be used by the Al Umma activists in their efforts to get away.

Among those in the Coimbatore jail was a hard-core activist, identified as Mujbir Rehman, who the sources claimed had confessed to police interrogators after his arrest that he had planted explosives in two-wheelers at Sir Shanmugham Chettiar Road on February 18 last year, when Home Minister L K Advani was to visitCoimbatore.

Nine persons were killed and 30 wounded in the explosion, which severely damaged several vehicles, including a police van.