mnesty International has condemned the hanging in Iran of Reza Hejazi, who was executed for a crime he committed when he was under 18 years old.
Hejazi was aged 15 in 2004 when he was among a group of people involved in a dispute which resulted in a man being fatally stabbed.
He was hanged in the city of Isfahan on Tuesday, Iranian media said.
Amnesty says the execution of juvenile offenders is prohibited under international law.
The rights group also says the Iranian authorities failed to give 48 hours' notice of the execution, in contravention of Iranian law.
Hejazi's lawyer, Mohammad Mostafaie, told the BBC Persian Service that he had gone to Isfahan prison on Tuesday after hearing from Reza Hejazi's family that he was about to be executed.
After spending several hours there, he was told the execution had been postponed and he passed this news on to the family.
Mr Mostafaie said he was on his way back to his office in Tehran when he was told by journalists that Reza Hejazi had been hanged.
According to Amnesty International, the execution brings the number of juvenile offenders put to death in Iran this year to five, with 132 more on death row.
In 2007, Iran was one of only three countries to execute such offenders. So far this year it is the only country known to have done so.
Last year, Iran was second only to China in the number of overall executions it carried out for crimes including murder, rape, drug trafficking and armed robbery.
Last month, 29 criminals were executed in Teheran's Evin prison on a single day.