The mayor of Hangu said two people were killed Friday in Hangu and two more in the nearby village of Ibrahimzai, the BBC reported.
The army reported heavy fighting between Muslim factions overnight, despite a 24-hour curfew imposed after a suspected suicide bomber attacked a bazaar Thursday during the celebration of Ashura, the most important Shiite holy day.
Feroz Khan, district health officer for Hangu, said 65 people were wounded in the attack and the rioting that followed, the BBC reported.
In neighboring Afghanistan, violence between hundreds of Shiites and Sunnis in the western city of Herat left at least five dead and 51 injured.
Ashura marks the death of the Prophet Muhammad's grandson Imam Hussein, which led to the split between Shiite and Sunni Muslims.