Human rights groups point that confessions were extracted under torture and the alleged crime was committed when the convict was 17, a minor.
Rights groups and the UN have accused Iran of flouting its international obligations after executing a young man convicted for a murder he was accused of committing as a minor.
"The execution of Arman Abdolali is an international crime," said Mahmood Amiry Moghaddam, head of Oslo-based NGO Iran Human Rights (IHR), which monitors executions in Iran.
He called for President Ebrahim Raisi, judiciary chief before his election this year, to be brought to account for Abdolali's execution.
A spokes for the UN Human Rights Office said it was "deeply alarming and shocking that his hanging went ahead despite interventions by numerous parties" that included direct contact between the UN and Iran.
No fair trial, no body
Abdolali, 25, was executed at dawn in the Rajal Shahr prison on Wednesday over allegedly killing his girlfriend when he was 17.
IHR said Abdolali confessed at the time of his arrest, but a body was never found and he later retracted.
"Besides being executed for an alleged offence committed at under 18 years of age which is a violation of international law, Arman was sentenced to death based on confessions extracted under torture, without a fair trial and due process," he said in a statement.
He was previously being transferred to solitary confinement for hanging six times as what IHR called a form of "psychological torture".
He not given the chance of a final meeting with his family, the organisation said.
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