An Indonesian widow who was allegedly gang raped by a group of vigilantes as punishment for having an affair with a married man, is facing public caning for violating Islamic law.

The head of Islamic Sharia law office in the eastern town of Langsa, in the conservative Aceh province, said that the 25-year-old woman and her 40-year-old lover should be punished for adultery.

"We want the couple to be caned because they violated the religious bylaw on sexual relations," Ibrahim Latif told the Jakarta Globe.

"They've confessed to having sex on several previous occasions, even though the man is married and has five children."

He said that since the woman was raped after the adultery, the violence was not to be considered a mitigating circumstance, so her punishment would still be carried out according to Sharia Law.

The woman said she was raped by eight men who surprised her as she was having sex with her lover in her house.

The man was tied up and beaten while she was repeatedly raped. The attackers then threw a bucket of sewage over the couple, before handing them over to the local sharia police. The pair face up to nine strokes of the cane each.

As the rape allegations emerged, three gang members, including a 13-year-old were arrested.

Police said they are hunting for the others. The attackers face up to 15 years in prison but are not at risk of caning as they have not been charged under Sharia law.