The latest, at a naval college in Lahore Tuesday, was the fourth in five days.
Foreign jihadists in an ungoverned tribal belt kill leaders, recruit locals.
Intelligence reports find that al Qaeda may be using the region to launch more sophisticated terror attacks.
Director of CIA says "no reason" to doubt Islamist group's responsibility, echoing findings of Scotland Yard.
The attack is a setback for the Army and is raising concerns ahead of next month's elections.