Two Pakistani men and a woman were stoned and then shot to death for committing adultery, an official said.
A jirga, or council of elders, in the Khyber tribal agency near the Afghan border ordered the execution of the three yesterday, two days after they were caught and handed over to the council for judgement, residents said.
"Allah Noor, Shehzad and the woman, Tasleem, were caught red-handed in a compromising position by activists of the Lashkar Islami religious group," said one resident.
Hundreds of people threw stones at them before relatives of the two accused men shot them dead.
Sex out of marriage is a crime in predominantly Muslim Pakistan and punishable by stoning to death under Islamic laws, although that punishment has never officially been handed down.
But in remote, semi-autonomous tribal areas, jirgas often decide on such issues. Hundreds of people are killed every year in Pakistan, most in rural communities, after being deemed to have dishonoured their families.
A government official in the area, southwest of Peshawar, capital of North West Frontier Province, said the accused had confessed to the jirga, and that authorities had not intervened.