Human Rights Watch (HRW) is urging Iran to issue an immediate moratorium on executions following revelations of what it calls "unlawful or politically motivated executions."
The New-York-based watchdog's call comes after Iran executed 16 people on October 26 in what prosecutors said was "retaliation" for the killings of border guards along the Iran-Pakistan border.
HRW says two Kurdish prisoners were executed on the same day for their alleged links to an armed group.
The group says more than 400 executions in Iran have been documented in 2013 in a judicial system "rife with due process failures."
On October 28, Amnesty International said the recent surge in executions shows that Iranian authorities "continue to rely on state-sponsored killing."
The London-based organization also warned that two Kurdish inmates were at "imminent risk" of being executed.