The incident took place shortly after the victims left Spai, a predominantly Shiite village in the Orakzai tribal area, said local government official Jamil Khan. They were headed for the nearby district of Kohat, he said.
Pakistan is a majority Sunni Muslim state, and most Sunnis and Shiites live peacefully together. But the country has a long history of sectarian attacks by extremists on both sides.
Attacks by Sunni militants on Shiites have been on the rise over the last year, especially in southwestern Baluchistan province.
The Sunni-Shiite schism over the true heir to Islam's Prophet Muhammad dates back to the seventh century.