At least 15 people were injured in a blast at a mosque in the northwestern Pakistani city of Dera Ismail Khan today,witnesses said. Witnesses and local residents said a grenade was lobbed into the mosque while a group of people were praying inside. The blast injured about 15 people who were taken to a local hospital. Dera Ismail Khan has witnessed several bomb attacks in the past few months. The city is located near South Waziristan tribal region and Bannu and Tank districts of the North West Frontier Province,where the Pakistani Taliban have a strong presence.