An Iranian woman whose sentence of execution by stoning for adultery provoked a worldwide outcry will instead be hanged for murder on Wednesday, a human rights group said.

"The authorities in Tehran have given the go-ahead to Tabriz prison for the execution of Iran stoning case Sakineh Mohammadi Ashtiani," the International Committee against Stoning, a German-based campaign group, said on its website.

"It has been reported that she is to be executed this Wednesday, 3 November."

Officials in Iran were not available to confirm or deny the report.

Ashtiani's stoning sentence was suspended after prominent political and religious figures called it "medieval", "barbaric" and "brutal". Brazil, a close ally of Iran's, offered to give the 43-year-old mother of two asylum.

A government spokesman said in September Ashtiani's adultery conviction was under review but the charge of being complicit in the murder of her husband was still pending.

Under the Islamic law in force in Iran since the 1979 Islamic Revolution, murder is punishable by hanging, adultery by stoning.

President Mahmoud Ahmadinejad fended off questions about the case from reporters when he attended the UN General Assembly in September, saying it had been fabricated by hostile Western media and called the United States hypocritical for its record on executions.

The case has worsened relations between Iran and the West, which are locked in a dispute over Tehran's nuclear programme, and was further complicated last month when two Germans were arrested in Iran while conducting an interview with Ashtiani's son.

The men entered Iran with tourist visas and were not authorised to act as journalists, judicial officials said. The German government is trying to secure their release.

In August, Iranian television aired an interview with a woman it said was Ashtiani admitting a relationship with a man who then murdered her husband. The International Committee Against Stoning, called the TV show "toxic propaganda".

The United States has imposed sanctions on eight senior Iranian officials, including the commander of the Revolutionary Guards and several cabinet ministers, for human rights abuses.

That is in addition to the sanctions over Iran's nuclear activities which it fears is aimed at making an atomic bomb, something Tehran denies.

According to Amnesty International, Iran is second only to China in the number of executions it carries out. It put to death at least 346 people in 2008.