Sakineh Mohammadi Ashtiani's first lawyer fled Iran to Norway after an arrest warrant was issued for him [EPA]

An international rights group is urging Iran to release the son and the lawyer of an Iranian woman who has been sentenced to death by stoning for adultery.

The call by Amnesty International (AI) comes as fears grow that Sakineh Mohammadi Ashtiani, 43, could also be soon executed for murder.

The London-based group says Ashtiani's son, Sajjad Qaderzadeh, and lawyer Houtan Kian were arrested on October 10, along with two Germans seeking to interview the son.

AI's Iran expert Ann Harrison says the detentions are "very worrying" and that with both her son and lawyer arrested, Ashtiani has no one left to defend her.

The Iranian State Prosecutor told AI that Qaderzadeh is under investigation involvement with "anti-revolutionary groups abroad" while Kian was arrested for being in possession of three forged identification cards.

Stoning sentence

Ashtiani's case has sparked protests around the world, with critics accusing the Iranian government of sexism and brutality. 

She was convicted of adultery in 2006 after she was found guilty of having "illicit" relationships with two men following her husband's 2005 murder. She was also found guilty of conspiring to kill her husband with one of the men, her husband's cousin.

Ashtiani's "confession" was broadcast on Iranian television in August, although her face was blurred and her voice was dubbed from Turkish (Ashtiani's native language) to Farsi.

Kian said that Ashtiani had been "severely beaten up and tortured" until she's agreed to confess on camera.

Her case triggered an international outcry and elevated tensions between Iran and the West. Tehran temporarily suspended the stoning verdict, suggesting Ashtiani might be hanged instead.