If you ask Iranian judiciary they deny torturing prisoners, in fact not only they deny practicing torture in Iran also they condemn torture and speak against of other countries that practice torture. So what do they practice really?! Nothing really, they torture but they don’t call it torture. They use an Arabic-Islamic word called “Tazir” which refers to punishment instead of “torture”. So simply they don’t torture but they do punish, lash, beat, kick, cut, rape and etc. all happens under definition of “Tazir”.
Bahman Aghai Diba, Ph.D. International Law wrote:
When an interrogator wants to torture a person, especially the political ones, he goes to Mullah Judge (called Hakem-e Shariah) and asks him to give permission for let say inflicting 50 lashes to get confession from the suspects. If that works, it is the mission accomplished. If not, he can go back and get permission from the Mullah Judge for as many and as hard lashings that he likes.
While there is a great difference between a gentle stroke of the lash and the sever strike that gushes blood out of the body of the miserable subjects of torture, there is no criteria or system to administer or observe how the permission of the "Tazir" is implemented. The interrogators implement them as they wish. Sometimes the lashing, especially against women and young prisoners lead to sever injuries, damaging the internal organs and permanent loss of the physical functions.
Hat tips: Rotten Gods: Islamic Iran Tortures Activists, Tazir: the Islamic Torture in Iran