A joint interrogation team (JIT), consisting of police and Rangers officials, on Monday carried out a search operation in Kot Lakhpat Jail.
The operation was started in the wake of the recent attack on Dera Ismail Khan Jail, in which almost 250 prisoners managed to escape.
Initial investigation suggested that prisoners in the DI Khan jail possessed cell phones through which they had maintained contact with the terrorists.
According to officials, information of a terrorist attack on the jail had been received. Barracks of prisoners were searched in the operation.
Earlier on Saturday, security at the Hyderabad Central Jail, a site of frequent jail riots, was heightened.
On Sunday, Rangers carried out a security exercise in the Karachi Central Jail.
