Amnesty, which opposes the death penalty under any circumstances, said an Iranian man had been stoned to death in July last year for committing adultery, despite a moratorium being imposed on such executions in 2002.

The woman he was convicted of committing adultery with still faces the threat of being stoned, a practice that involves the woman being buried up to her breasts in sand and then pelted with stones until she dies.

"Amnesty International is calling on the Iranian government to abolish immediately and totally execution by stoning and to impose a moratorium on the death penalty," the rights group said in a 30-page report on the practice.

"Iranian law prescribes that the stones are deliberately chosen to be large enough to cause pain, but not so large as to kill the victim immediately ... It is a particularly grotesque and horrific practice."

While stoning is used relatively seldom in Iran, it is the favoured form of execution in cases involving adultery and has a disproportionate impact on women, according to Amnesty.

Iran has one of the highest rates of execution in the world. In 2006, 177 people were put to death, mostly by hanging. Last year, that number was expected to be exceeded, with 124 people executed in the first seven months of the year.

As well as calling for the abolition of stoning and a moratorium on the death penalty, Amnesty also urged the Iranian government to decriminalise adultery, which is not illegal in the majority of countries.