A United Nations Special Rapporteur has expressed outrage at the execution of man in Iran who received the death penalty as a child.

Alireza Tajiki was arrested in 2012 at the age of 15 and sentenced to death at the age of 16 in 2013.

The UN says he was executed on August 10th, despite interventions by experts who said the death penalty should never be used against a child.

Special Rapporteur Asma Jahangir said: "I am distressed in the extreme to learn that this execution has gone ahead despite twice being postponed on previous scheduled dates".

Human rights experts stressed that Mr Tajiki's death penalty was upheld following judicial procedures which did not meet acceptable international standards of a fair trial or due process.

"I am deeply concerned that the court relied on the use of forced 'confessions', which were reportedly extracted using torture, including beatings, floggings and suspension by the arms and feet,", Ms Jahangir said.

"There has been no investigation into these torture claims.

"Mr. Tajiki also suffered violations of his rights to a defence, for example by being denied access to a lawyer throughout the entire investigation process and being held in solitary confinement for 15 days without access to his family."

Ms Jahangir added: "This treatment would be unacceptable for an adult, but for a child suspect to have been convicted after such grave rights abuses, and then to be executed despite all interventions, is truly shocking."

The death sentence against Mr Tajiki was quashed in 2014, but he was re-sentenced to death by the Provincial Criminal Court of Fars.

This court ruled that he had sufficient "mental maturity" for an understanding of his alleged crime to be executed.

That verdict was later upheld by Iran's Supreme Court.