Saman Naseem, 22, is scheduled to be executed Thursday after being found guilty of membership of the rebel Party of Free Life of Kurdistan (PJAK) and involvement in armed confrontations with the Revolutionary Guards.

He was 17 at the time of his arrest and was sentenced to death in April 2013, allegedly after being tortured.

"Time is running out for Saman Naseem. The fact that Iran is willing to execute a man who was tortured to confess to a crime he is accused of having committed when he was a child shows the state of injustice in the country," said Amnesty International's Hassiba Hadj Sahraoui.

"These wrongs can never be undone, but it is not too late to immediately stop Saman Naseem's execution and initiate a thorough judicial review of his case," she said in a statement.

The International Federation for Human Rights also demanded a halt to the execution, and called for the overturning of Naseem's death sentence, which it said is illegal under international law.

"The continued detention and ill-treatment of Saman Naseem is unacceptable and is a violation of international law," said FIDH president Karim Lahidji.

"Saman's death sentence must be immediately repealed and he must be given a fair trial that meets international standards."

The FIDH alleged that Naseem was denied access to lawyers at the time of his arrest and that his original conviction was based on "forced confessions obtained through torture".

It said Iran is a signatory to the UN Convention on the Rights of the Child which prohibits the death penalty for juvenile offenders.

In October, the United Nations expressed concern about what it described as a "surge in executions" in Iran as part of a worsening human rights situation under reformist President Hassan Rouhani.