Amnesty International has urged Tehran to spare the lives of six Sunni men sentenced to death.
Amnesty said the six are set to be hanged, as soon as March 4, and have gone on a hunger strike.
The human rights watchdog said the six were sentenced to death after being found guilty of the offense of "enmity against God."
The prisoners' family members are heading to the prison in Karaj where they are being held after prison authorities told them they could have one final visit with their loved ones.
Four of the men – Hamed Ahmadi, Jahangir Dehghani, Jamshid Dehghani and Kamal Molaee – are accused of killing a senior Sunni cleric in September 2009, but they claim they were arrested several months before the killing.
They are among 33 Sunni men currently on death row in Iran, which is mainly Shi'a.
All of them maintain that they were targeted solely because they practiced or promoted their faith.