The United Nations’ top official for human rights has criticized Iran for hanging up 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, leading to a “grave injustice” being committed.

Iran executed up to 20 Kurdish Islamists on Tuesday who were suspected of attacks on security forces, drawing condemnation from rights groups which said the convictions may have been based on forced confessions.

They were convicted of killing two Sunni Muslim clerics, several police and wildlife guards, abducting a number of people and carrying out armed robbery and bombings in western Iran, state news agency IRNA said.

Zeid said the men had been executed for “purported terrorism-related offences” and that reports suggested most if not all were from a minority group – Sunnis from the Kurdish community.

“The application of overly broad and vague criminal charges, coupled with a disdain for the rights of the accused to due process and a fair trial have in these cases led to a grave injustice,” Zeid said in his statement.

Shahram Ahmadi, one of those hanged, was alleged to have been beaten and coerced into signing a blank piece of paper on which his false confession was recorded, Zeid said.

Iran is one of the world’s top executioners, international rights groups say. Human Rights Watch said this week that Iran had executed at least 230 people this year.

Hassan Afshar, a 19-year-old who was 17 when he was arrested and convicted of rape, was executed last month, Zeid said.

“The execution of juvenile offenders is particularly abhorrent and I urge Iran to respect the strict prohibition under international human rights law against this practice,” he said.