Pakistani rangers cordon off the blast site in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)

Pakistani rangers gather around a destroyed vehicle at the blast site in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)

Pakistani rangers cordon off the blast site in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)

Rescuers gathered around a body at a hospital in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)

Pakistani rangers cordon off the blast site in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)

Rescuers transfer an injured man to a hospital in southern Pakistani port city of Karachi on April 3, 2013. At least three security personnel were killed and seven others injured on Wednesday evening in a hand grenade attack in Pakistan's southern port city of Karachi, local media reported. (Xinhua/Arshad)