Two lovers were tied to trees and stoned to death for adultery by angry relatives in a Pakistani village this weekend.

Police said the couple, in their early 40s, were killed in a barrage of rocks thrown by relatives of the woman in Donga Bonga village in central Punjab province on Sunday.

"It was a case of honor killing and we have arrested two brothers of the woman,'' local police chief Zafar Bokhari said.

Bokhari said the woman's family was annoyed because of her alleged affair with a man from the same village and planned the murder with the help of other relatives.

Donga Bonga police officer Haji Mohammad identified the woman as Ellahi Hussain and the man as Hafeez Shah.

Mohammad said the attackers dragged them from the house with a rope tied around the couple's neck to the trees, where they smashed their heads with stones and bricks.

Police reached the scene after some villagers heard the cries of the couple and contacted the authorities.

"We saw them sleeping together and we could not tolerate this immoral act and decided to punish them,'' the woman's brother, Maqbool, told the police in custody.

Mohammad said police were conducting raids to arrest two others relatives who allegedly took part in the killing.

About 4,000 people, mostly women, have been killed in deeply conservative rural Pakistan in recent years in the name of protecting family honor in the midst of allegations of illicit sexual relationships.

In 2005, Pakistani President Pervez Musharraf had a law enacted by parliament which introduced the death penalty for honour killings.