Sources, including a first responder and a security officer, told CNN the attack began with a suicide bombing. After an explosives-laden car was driven into the Inter-Services Intelligence compound, men armed with guns and grenades assaulted the compound.
At least 35 people were wounded, many of them critically, GEO TV reported.
The Barrage Colony houses the local offices of the ISI and the homes of judges and police officers.
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Syrian Al Qaida group executes Lebanese soldier