The men had said during their trial that they had been in contact with the Islamic State in neighboring Afghanistan and helped organize the attack on the Shah Cheragh shrine.
Shahrouz Sokhnori was sentenced to death and found guilty of corruption for trafficking women across the Middle East and Asia.
The report alleges that only 12% of state executions were reported by officials.
The Iranian foreign ministry announced it has summoned the UK ambassador over what it called London's "meddling in Iran's national security realm."