At least 50 were killed in the suicide attack on the Sunni mosque in Khyber Agency.
It's unclear who was behind the attack, which took place in tribal region West of Peshawar known as the Khyber Agency. Security forces tasked with protecting NATO supply lines were among those praying and subsequently killed at the mosque, according to local reports.
By attacking a packed Sunni mosque at Friday prayers, the perpetrators showed a brazen disregard for popular sentiment in the region, analysts say.
"I think people in the frontier will be scared to send their children and men to the mosque. And I think the moderate sort of religious people in Pakistan will be calling for some action against these people," says security analyst retired Brig. Gen. Mahmood Shah.