The United States on Thursday urged Iran not to stone to death a woman convicted of adultery, calling the punishment "barbaric."

"Stoning as a means of execution is tantamount to torture. It's barbaric and an abhorrent act," State Department spokesman Mark Toner told reporters.

"We condemn in the strongest terms the use of the practice of stoning anywhere it occurs as a form of legalized death by torture," he said.

Sakineh Mohammadi-Ashtiani, a 43-year-old Kurdish woman, faced an execution by stoning which may be imminent, according to Amnesty International. The rights group said she was already given 99 lashes for adultery.

Toner said that the United States was "deeply troubled" by the case.

"We call on the Iranian authorities to live up to their due process commitments under the International Convention on Civil and Political Rights," he said, referring to the UN treaty drafted in 1966.

Iran's planned stoning execution has led to condemnation around the world, with British Foreign Secretary William Hague saying that Tehran would "disgust and appal" the rest of the world.

The United States ended diplomatic relations with Iran after the 1979 Islamic revolution overthrew the pro-Western shah.

President Barack Obama has offered dialogue with Iran to repair relations but also criticized the clerical regime's human rights record, including its clampdown on opposition protests after last year's disputed election.