To get around this, the Islamic Republic's judiciary often issues death sentences for minors and executes them once they turn 18 -- although there have been cases where criminal offenders have been executed while they are still minors.
The United Nations Committee on the Rights of the Child urged Iran in a report on 28 January to take the necessary steps to immediately suspend death sentences imposed on persons convicted of crimes before the age of 18.
The UN says earlier that month, Iranian officials issued a study saying such executions had been suspended. But on the same day that study was issued, a minor was executed in Iran.
The International Federation of Human Rights and Amnesty International say it is time for Iran to bring its law and practice in line with its international obligations.
Doctor Abdol-Karim Lahidji is the vice president of the Paris-based International Federation of Human Rights.
"The Islamic Republic, since its establishment 25 or 26 years ago, has only joined one international convention and that is the Convention on the Rights of Child, and it should be committed to its obligations under it. The UN committee made many recommendations to Iran in regard to children's rights and topping them is the issue of child execution," Lahidji said.
Under the UN convention, any person under the age of 18 is considered a child. Last year Amnesty International recorded three executions of child offenders in Iran.
One of them was a 16-year-old girl who was hanged in public for having what was termed "illegitimate sexual relations."
Lahidji says real figures about the cases of juvenile execution could be higher.
"In light of the fact that there are no official figures from the Islamic Republic and the figures we get are from the Center of Human Rights Defenders or other sources in Iran, unfortunately we can't categorically say if there were other cases during the last year, especially in remote provinces where such things don't get any coverage even in the few newspapers that -- under the current conditions of censorship by the judiciary -- [are able to] publish such news," Lahidji said.
Last October, some 20 Iran-based human-rights groups, including the Center of Human Rights Defenders, founded by Nobel Prize winner Shirin Ebadi, called on the head of Iran's judiciary not to sentence minors to death.
Ebadi, who has been fighting for the improvement of women's and children's rights in Iran, had called for a rally to protest against the practice -- but the demonstration was banned by authorities.
The International Federation for Human Rights say 25 juvenile offenders currently held in Iranian prisons are facing execution. Iran's judiciary announced last fall that death penalties for convicted criminals younger than 18 years will be banned.
Shiva Dolatabadi is the director of the Society for the Rights of Children in Tehran. She says a bill outlawing juvenile execution has been sent for review to the parliament.
"As far as we have been able to follow the issue, the bill has been sent to the parliament, but we haven't heard about it being finalized. It seems that the good news we heard -- that these things are not going to happen anymore -- was when the bill was sent to the parliament, but it hasn't become a law yet," Dolatabadi said.
Experts say that if the bill becomes law it should clearly prohibit juvenile execution and not give judges the power to choose whether or not to assign such a sentence.
The UN Committee on the Rights of Child has also called on Iran to suspend the imposition and execution of all forms of torture and cruel, inhuman, or degrading treatment, such as flogging and stoning for crimes committed by underage people.
Dolatabadi says flogging sentences are being issued for boys and girls who socialize with each other.
"Most of it is connected with relations between girls and boys, which according to [legal] definitions here can easily become a crime. We hear a lot about sentences [of flogging] being issued in connection with people going to parties and such things. However, we don't know to what extent [the sentences] are being applied. We don't have enough figures," Dolatabadi says.
In recent months, international pressure has been growing on Iran to end the execution of minors. In October, the EU parliament condemned Iran for issuing death sentences for minors.
Lahidji, from the International Federation of Human Rights, believes such pressure will help convince Tehran to halt the practice.
"International pressure has always been effective, even though the Islamic Republic denies it. Three young people accused of hijacking a plane were due to be executed two weeks ago, but because of [international] campaigns their execution was fortunately halted," Lahidji said.
Iranian officials have not yet reacted to the UN Committee on the Rights of the Child report.