A 23-year-old woman made a frantic phonecall to her mother begging for help before Iran authorities held a rushed execution - disregarding a stay-of-execution and allegedly without informing her lawyer.

'Mother they are going to execute me, please save me,' Delara Darabi screamed, before a prison official grabbed the phone and told her mother: 'We are going to execute your daughter and there's nothing you can do about it.'

She was just 17 when she confessed to the killing of her father's cousin, before retracting her confession, saying she had been defending her 19-year-old boyfriend.

Now international aid agencies and human rights group have joined in a chorus of outrage and disapproval over Iran's 'illegal' execution, calling on the U.N. to hold an international tribunal to bring those responsible for justice'.

The U.N. Convention on the Rights of the Child, which Iran has signed, bans capital punishment for offenders who committed crimes before their 18th birthday.

Miss Darabi has become a figurehead for human rights, and her case gained widespread attention after moving paintings and drawings that she made in her prison cell were shown around the world.

She told a judge that she had initially confessed because her boyfriend, who she said carried out the killing, told her that, as a minor, she would not be executed and she could save him from being put to death.

Lawyer Mohammad Mostafaei said Darabi called her parents just moments before the execution on Friday. He quoted her as saying, 'Oh, Mother, I see the hangman's noose in front of me. They are going to execute me. Please save me.'

He added: 'They took Delara to the gallows with nobody around her.

'They put the rope on her delicate neck. I do not know who the cruel person was to pull the chair from under her feet.'

Iran executed eight 'juvenile offenders' last year, and 42 since 1990, according to Amnesty International.

While a few other countries are known to have executed juvenile offenders in recent years - Saudi Arabia, Yemen, Sudan and Pakistan - Iran has accounted for more than two-thirds of such executions in the past four years, according to rights groups.

Human Rights Watch deputy director Zama Coursen-Neff said: 'Iran continues to deny that it executes juvenile offenders, but the secret nature of this execution demonstrates that the government knows that these killings are illegal and shameful in the eyes of the world.'

Her paintings are generally made up charcoal lines depicting anguished faces, splashed with red to highlight the 'hell of incarcaration'.

Delara once said: 'I try to defend myself using colours, forms and words. These paintings are my swear to what I have not done.

From behind the walls, I say hello to you, who has come to see my paintings.'

The U.N. Convention on the Rights of the Child, which Iran has signed, bans capital punishment for offenders who committed crimes before their 18th birthday.

As her family buried her at the weekend and the EU joined the chorus of criticism against the Iranian authorities, the human rights lawyer, Mr Mostafaei, recalled the personal gift Ms Darabi had bestowed on him.

'She painted a picture of an old man playing the violin,' he said. 'I did not know that he was playing her death song.'

Iranian law requires authorities to inform a prisoner's lawyer at least 48 hours before an execution, but Mostafaei said he was not given warning that the sentence was to be carried out.

The woman's parents were not allowed inside the prison to meet her for a last time, Mostafaei said.

'She was denied a legal right guaranteed under the law,' he said. 'The hasty execution and the ignoring of legal provisions suggests that some authorities were happy to put an end to her life,' he said.

Mostafaei said the execution of juvenile offenders is a 'gross violation of international law' and a 'breach of Iran's international obligations and commitments'.

The European Union also condemned Darabi's execution, saying the punishment ran ''counter to the international commitments that Iran has voluntarily accepted.'

Mostafaei said the court did not seriously consider his arguments in the woman's defence.

For example, he said, Darabi was left-handed, while all the evidence suggests the crime was committed by someone who was right-handed.

The execution of the young woman is another damaging blow to President Barack Obama's attempts to thaw US relations with the Islamic regime.

'Amnesty International is outraged at the execution and particularly at the news that her lawyer was not informed,' said Hassiba Hadj Sahraoui, deputy chief for the Middle East and North Africa.

'This appears to have been a cynical move on the part of the authorities to avoid domestic and international protests which might have saved Delara Darabi's life.

'This indicates that even decisions by the Head of the Judiciary carry no weight and are disregarded in the provinces.

'Amnesty International does not consider her trial to have been fair, as the courts later refused to consider new evidence which the lawyer said would have proved she could not have committed the murder.'

Mahmood Amiry-Moghaddam spokesman of Iran Human Rights group, said: 'Iranian leadership and judiciary must be held responsible for execution of Delara Darabi.

'Lack of strong and sustainable reactions from the world community is one of the main reasons why Iranian authorities continue execution of minors.

'Iranian authorities have learned that their violations of the human rights lead just to some verbal protests from the world community, without any practical consequences

'It is the time that UN and world community show that UN’s conventions are more than just formalities.

He said the UN and EU 'should condemn Delara’s execution and put sanctions on the Iranian authorities'.

Stop Child Executions also condemned the 'illegal' execution.

They called for the 'formation of an independent international tribunal to look in to the case and to bring all those responsible for the unjust sentencing and execution to international justice.'