Two men and a woman were stoned and shot to death in northwestern Pakistan on the orders of a tribal council that found them guilty of adultery, an official said Thursday.

Activists from a radical Islamic group detained the three on Monday in a house in Belod, a village in the Khyber tribal agency near the Afghan border, said Fazel Mehmood, a local government official.

The activists from the Lashkar-Islam group put a woman called Tasleema and two men, identified as Noorullah and Shehzad, before a jirga, or tribal council, on Wednesday, where elders found them guilty of adultery, Mehmood said.

The trio then were taken to an open field near the village, their hands tied behind their backs, where more than 100 people had gathered. Some members of the crowd stoned them, then others stepped forward with assault rifles and shot them to death, Mehmood said.

Mehmood said the government had only learned of the incident on Thursday and that, in any case, it had no power to interfere with "tribal traditions" in the semiautonomous tribal belt.

Pakistani authorities have only a limited grip on its tribal areas along the rugged, northwestern frontier with Afghanistan, which is populated by ethnic Pashtuns with an ultra-conservative view of Islam shared by Taliban fundamentalists.

However, such stark incidents of tribal justice — particularly stoning people to death — are uncommon.

In the most notorious example, a Pakistani woman was gang raped at the order of tribal council in the eastern province of Punjab in 2002 to punish her family for her brother's alleged affair with another woman. The victim, Mukhtar Mai, has since become an icon for women rights.