Iranian media say a 34-year-old man had a hand chopped off as punishment for stealing livestock in the northeastern province of Razavi Khorasan.
The local, state-sponsored newspaper Khorasan reported that the amputation took place on January 17 in the central prison in the provincial capital, Mashhad.
The man, referred to as A. Kh., was transferred to a medical center after the punishment was carried out, the paper said.
He was sentenced to hand amputation six years ago, and the sentence was later upheld by an appeals court.
In a statement, Amnesty International said that such an "unspeakably cruel" punishment showed the Iranian authorities' "complete disregard for human dignity."
"There is no place for such brutality in a robust criminal justice system," said Magdalena Mughrabi, Deputy Middle East and North Africa Director at the London-based rights group.
"Amputation is torture plain and simple, and administering torture is a crime under international law," Mughrabi added.
The Iranian authorities have defended amputation as the best way to deter theft.
In 2017, dozens of amputation sentences were imposed in Iran and subsequently upheld by the country's Supreme Court, according to Amnesty International.
Judicial authorities also continued to carry out punishments such as flogging and blinding.