The grenade explosion took place in Mawrah, Lower Orakzai Agency, when the jirga was being convened to discuss the family dispute between a man identified as Tehwar Hussain and his rivals.
As the situation got tense, Hussain threw a hand grenade towards the rival party, an official of the political administration from Kalaya, headquarters of Lower Orakzai, said.
The hand grenade exploded, killing Hussain and two other tribesmen on the spot, Express Tribune reported.
The official identified the other deceased as Syed Itwar Hussain, Syed Malik Hussain and Syed Kazim Hussain, while the name of the fourth tribesman could not be ascertained.