The Vatican has hinted that it may use behind-the-scenes diplomacy in a bid to save the life of an Iranian widow sentenced to be stoned for adultery.

In its first public statement on the case, which has attracted worldwide attention, the Vatican condemned stoning as a particularly brutal form of capital punishment.

Vatican spokesman the Rev Federico Lombardi said the Catholic Church opposed the death penalty in general.

It is unclear what chances any Vatican bid would have to persuade the Muslim nation to spare the woman's life. Brazil, which has friendly relations with Iran, was rebuffed when it offered her asylum.

Sakineh Mohammadi Ashtiani was convicted in 2006 of adultery. In July Iranian authorities said they would not carry out the stoning sentence for the time being, but the mother of two could still face execution by hanging for adultery and other offences.

Her son Sajad told Italian news agency Adnkronos that he was appealing to Pope Benedict XVI and to Italy to work to stop the execution.

Mr Lombardi said no formal appeal had reached the Vatican but he hinted that diplomacy might be employed to try to save Ms Ashtiani. Mr Lombardi said the Holy See "is following the case with attention and interest".

"When the Holy See is asked, in an appropriate way, to intervene in humanitarian issues with the authorities of other countries, as it has happened many times in the past, it does so not in a public way, but through its own diplomatic channels," Mr Lombardi said in a statement.

In one of the late Pope John Paul II's encyclicals in 1995, the pontiff laid out the Catholic Church's stance against capital punishment.

John Paul interceded in several high-profile cases of death-row inmates in the US. One of the first was the case of Paula Cooper, who was convicted of murdering her elderly bible teacher when she was 15 but spared the electric chair by Indiana in 1989. But that same year, a papal appeal for clemency to Cuba to spare a war hero and three other Cuban officers convicted of drug trafficking from the firing squad went unheeded.