At least 23 people were killed and dozens more injured on Friday in a suicide bombing during a gathering in Pakistan's tribal region along the Afghan border, officials said.
The jirga, a meeting of some 500 of members of the Alikhel tribe was being held in Khadezai village of Orakzai district to raise a traditional army, or lashkar, against Taliban militants operating in the area.
"A young man sneaked into the gathering and blew himself up at around 04.30 pm (1030 GMT)," said a security official. "Twenty-three people have so far been confirmed dead and around 100 wounded."
According to the official, who spoke on condition of anonymity, the death toll might rise.
Pakistan's tribal region serves as a safe haven for Al Qaeda and Taliban militants launching cross-border attacks on US-led international forces in Afghanistan.
Pressed by Washington, Islamabad has recently launched offensives in some districts of the largely ungoverned tribal belt against the Islamic insurgents. It also encouraged local tribesmen to raise lashkars to oust militants from their regions.
Orakzai Agency, unlike other tribal districts, does not border Afghanistan directly and therefore has been relatively peaceful.
But for almost six months Taliban influence has been increasing in the area and militants have launched attacks on security forces. Twenty-five police recruits abducted in early September still remain in Taliban captivity.
Earlier this month Ferozkhel tribe, another tribe in the district, organised a lashkar and took positions on strategic hilltops to prey on extremists in their area.
Tribal fighters arrested eighteen insurgents, including four would-be suicide bombers, and two explosive-laden vehicles were seized.
Two militants' hideouts were destroyed two days ago, fuelling anger among the rebels.
The Alikhel tribe was expected to announce its support for the Ferozkhel people in the meeting hit by the suicide attack on Friday.