
The convoy, which was being escorted by security forces, was attacked in Char Khel village in the Kurram region.
All those killed were Shia Muslims, according to local officials, who said the death toll may rise.
The convoy was heading from Parachinar, in Kurram, to the main regional city of Peshawar when it was ambushed on Saturday in the predominantly Sunni region.
The Kurram tribal district has been a flashpoint for violence between the minority Shias and the Sunni community for several years.
Some reports put the number of dead at 18, including two women.
Jamshed Tori, who was wounded in the attack, told the Reuters news agency: "Militants attacked the last two vehicles in the convoy with automatic weapons near Char Khel village, killing 18 people."
A tribal leader, Mussrat Bangash, also confirmed the deaths.