Abdul Fatah Shafiq said the incident took place in the Kohistan-1 district leaving four civilians injured including a shopkeeper.
According to Shafiq, the explosive device had been planted on a bicycle in a sack and went off in front of the provincial National Directorate of Security (NDS) office.
However no NDS officials were hurt in the blast.
The wounded people were soon transferred to the hospital and their health conditions are reported to be stable.
No group including Taliban group have claimed responsibility behind the attack so far.
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