22 people were killed and 50 others were injured when a suicide bomber drove his car into main gate of the Shia imambargah in the central bazar of Parachinar, Kurram Agency.
A majority of those injured are critical and the death toll could be much higher.
So far, no one has claimed responsibility for the attack, and authorities said investigations were ongoing.
22 killed in blast in Pakistan
Response by the government
The Inter-Services Public Relations stated that the army also dispatched a helicopter to help evacuating the injured to hospitals.
Meanwhile, Pakistan's Interior Minister Chaudhry Nisar ordered an inquiry into the blast.
Nawaz Sharif expresses grief, vows action
Pakistan's Prime Minister Nawaz Sharif expressed regret at the incident. However, he added that "It is our responsibility to continue the war against terrorists...it is our national duty to continue this war until the complete annihilation of the scourge of terrorism from our soil."
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