Amnesty International has urged Iran not to hang a man for the second time, after he survived the first execution attempt.
The campaign group's website said the man was found alive at a morgue a day after being hanged, and that authorities said the prisoner would be hanged for a second time once his condition improves.
The 37-year-old, identified as Alireza M, was hanged in Bojnourd prison in northeast Iran last week after being convicted of drug offences.
According to official state media, a doctor declared him dead after the 12-minute hanging, but when the prisoner’s family went to collect his body the following day he was found to still be breathing.
He is currently in hospital, but a judge reportedly said he would be executed again "once medical staff confirm his health condition is good enough".
"The horrific prospect of this man facing a second hanging, after having gone through the whole ordeal already once, merely underlines the cruelty and inhumanity of the death penalty," said Amnesty's Philip Luther.
"The Iranian authorities must immediately halt Alireza M's execution and issue a moratorium on all others."
Alireza M is now reported to be in a "satisfactory" condition in hospital and a family member reportedly said the prisoner's two daughters were "the happiest of all" that he was alive.
He had reportedly been sentenced to death for drug trafficking by the Revolutionary Court, which tries drug offenders in Iran in proceedings that often do not meet international standards of fair trial, Amnesty said.
So far in 2013, the Iranian authorities are believed to have executed a total of at least 508 people, including 221 executions that have not been officially confirmed.
The majority of those executed were convicted of drug offences.