Campaigning MEP Anthea McIntyre has condemned Iran's killing of prisoner Mohammad Salas, executed in defiance of an 11th hour plea made by international parliamentarians.
She said: "The killing of Mr Salas marks a black day for justice, international rule of law and human rights."
The authorities in Tehran ordered the widely-condemned death sentence on Mr Salas to be carried out, just as a multi-party and cross-national group of MEPs was making a last-ditch plea for a stay of execution.
The Iranian authorities have spurned all previous appeals for the withdrawal of the death sentence and a retrial for Mr Salas.
Supporters say Mr Salas, a Gonabi Dervish, was wrongly convicted of the murder of three police officers when the case against him remained incomplete and unsubstantiated. Eyewitness and photographic evidence establishing his innocence was ignored by the court, while an alleged confession was extracted under duress.
He was sentenced to death by the Iranian Supreme Court in April.
A letter making a final plea to Tehran to halt the execution at the weekend was signed by 47 MEPs from 19 Member States and six political groups.
After learning of his death today Miss McIntyre, Conservative MEP for the West Midlands, said: "Mr Salas was a victim of religious persecution and suffered a blatant mistrial.
"He was considered by the Iranian state to be a religious enemy and he suffered a politically-motivated execution because of politics and his faith.
"We did all we could to stop the execution but the Iranian regime was set on it. They should now face the gravest condemnation from the EU leadership and the international community as a whole."