Iran's justice minister said a move to execute a convicted Iranian drug offender who has already survived a hanging is ill-advised, suggesting he would not face capital punishment again.

The statement by Justice Minister Mostafa Pourmohammadi, who does not run Iran's judiciary, followed international calls for Iran to spare the man, a 37-year-old named only as Alireza M.

New Iranian President Hassan Rouhani, a relative moderate, has sought to project a friendlier image to the West than his predecessor, the hardline conservative Mahmoud Ahmadinejad. Iran released prominent political prisoners, including human-rights lawyer Nasrin Sotoudeh, in September to wide global praise.

Iran carried out a hanging sentence on the man earlier this month in the northeast city of Bojnourd, according to human rights group Amnesty International. He was declared dead by a doctor but found a day later still alive in the morgue.

Amnesty has urged the Islamic Republic to halt the man's execution as well as all other death penalties.

Pourmohammadi said that efforts had been made to prevent another hanging.

"With great efforts made to not carry out a new execution of this convict ... we received a positive reply," Pourmohammadi said, according to state news agency IRNA. "The convicted individual who remained alive after execution is currently under an oxygen device, and if he remains alive, it is no longer expedient for the execution order to be carried out again."

Under the constitution, Iran's judiciary sentences criminals and confirms their punishment, not government ministers.

The head of Iran's judiciary, Ayatollah Sadeq Larijani, said on Wednesday the man could be spared on humanitarian grounds.

"One of the ways to deal with someone sentenced to execution who has seen death and tolerated hardships is a pardon, and such an individual who has specific conditions can be granted mercy and forgiveness by the Islamic system, and I ... will definitely do this," Larijani was quoted as saying by the ISNA news agency.

But Larijani said there were also legal grounds in favour of carrying out the death sentence again.

Iran carries out almost the highest number of executions of any country in the world, and rights groups have criticised the country for its use of the death penalty to dispense justice, especially for drug-related cases.

Amnesty said this month that Iran is believed to have executed at least 508 people in 2013, though 221 of them have not been officially confirmed.