The United Nations' top official for human rights has criticized Iran for executing 20 people this week.

A statement Friday by High Commissioner for Human Rights Zeid Ra'ad al-Hussein said there were "serious doubts about the fairness of the trials, respect for due process and other rights of the accused" before their executions.

On Tuesday, Iran's judiciary announced the executions, identifying those put to death as Kurdish Islamic extremists who were convicted of armed robbery, killing civilians and planning bomb attacks.

Zeid said reports suggested most, if not all, of those executed were Sunnis from Iran's Kurdish minority. Kurdish fighters increasingly have battled Iranian security forces in recent weeks in northwestern Iran, leading to fatalities on both sides.