The accident occurred near remote Tanger village around 6.15 pm, they said.
The driver of the load carrier, which was on its way to Tanger from Sawlakote, lost control while crossing a blind curve and rolled down into a gorge, officials said.
A rescue operation was immediately launched and all the three persons travelling in the vehicle were found dead, they said.
The deceased were identified as Bahar Din, Omkar Singh and Bhari Lal, all residents of Tanger.