LONDON (AFP) - International rights group Amnesty International condemned Iranian authorities Friday for what it said was the "unspeakably cruel" blinding of a man on the grounds of retribution.

The man was forcibly blinded in his left eye Tuesday under the principle of "qisas" - an eye for an eye - at a prison in Karaj, west of Teheran, Amnesty said.

The man had been convicted of throwing acid in another man's face in 2009, leading to a 10-year prison sentence, an order to pay blood money to the victim and the act of retribution.

"Punishing someone by deliberately blinding them is an unspeakably cruel and shocking act," said Raha Bahreini, Amnesty's Iran researcher, in a statement.

"This punishment exposes the utter barbarity of Iran's justice system and underlines the Iranian authorities' shocking disregard for basic humanity."

Iran's Tasnim news agency previously reported that the long-postponed punishment had finally gone ahead, but there has been no official comment.

The punishment of another male convict, who was scheduled to be blinded and made deaf in a similar act of retribution on Tuesday has been postponed until next month, Amnesty said.