The Vatican on Sunday raised the possibility of using behind-the-scenes diplomacy to try to spare 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 also decried stoning as a particularly "brutal" form of capital punishment.

Sakineh Mohammadi Ashtiani's son has told an Italian news agency he was appealing to Pope Benedict XVI and to Italy to work to stop his mother's execution. (Amnesty International/Associated Press)

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

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

Lombardi told The Associated Press that no formal appeal had reached the Vatican, but hinted that Vatican's diplomacy might be employed to try to save Ashtiani.

Lombardi said in a statement that 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," 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.

Meanwhile, Italy's foreign minister, Franco Frattini, told the ANSA news agency that while Italy respects Iranian sovereignty and isn't in any way interfering, "a gesture of clemency from Iran is the only thing that can save her."