The UN rights chief voiced outrage Monday at Iran's execution at the weekend of opposition figure Ruhollah Zam, and urged Tehran to halt its "alarming and increasing" use of the death penalty.

"I am appalled at the execution in Iran on 12 December of Ruhollah Zam," Michelle Bachelet said in a statement. "His death sentence and execution by hanging are emblematic of a pattern of forced confessions extracted under torture and broadcast on state media being used as a basis to convict people."