People gather at the attack site in southern Pakistani port city of Karachi, on March 30, 2013. Seven children were injured in hand grenade attack at a school in Pakistan's southern port city of Karachi on Saturday morning, local media reported. (Xinhua/Masroor)

Pakistani rangers cordon off the attack site in southern Pakistani port city of Karachi, on March 30, 2013. Seven children were injured in hand grenade attack at a school in Pakistan's southern port city of Karachi on Saturday morning, local media reported. (Xinhua/Masroor)

A Pakistani ranger stands guard at the attack site in southern Pakistani port city of Karachi, on March 30, 2013. Seven children were injured in hand grenade attack at a school in Pakistan's southern port city of Karachi on Saturday morning, local media reported. (Xinhua/Masroor)