The head of the Iranian opposition party Etemad Melli claimed on Sunday on his party's website that some young post-vote political prisoners had been sexually abused during detainment.
Mehdi Karroubi quoted released detainees as saying that some of the young females have been so harshly raped in jail that their genitals were torn.
In a letter to the head of the clergy body Experts' Assembly, Akbar Hashemi-Rafsanjani, Karroubi further claimed that young male prisoners had also been "brutally raped".
He added that the sexual abuses led to depression and serious psychological problems among the victims.
According to the Etemad Melli website, the letter to Rafsanjani was sent 10 days ago but as the former president, himself a member of the opposition, declined to reply to Karroubi's claims, the contents of the letter were made public on the party's website.
Protests over alleged fraud in the June 12 presidential elections led to the arrest of over 1,000 demonstrators whose majority has been released but more than 100 are still jailed.
Some of the prisoners were jailed in the Kahrizak prison in southern Tehran, also known as "Tehran's Guantanamo", which was closed down last month because it lacked the necessary standards for preserving detainees' rights.
Iranian police chief Esmaeil Ahmadi-Moqaddam on Sunday confirmed physical abuse in the Kahrizak prison, saying "there have been some violations in this centre and some of the officials there have not followed instructions".
The police chief said the head of the detention centre was arrested and then dismissed and two of the centre's guards were also dismissed.
Also Iran's Prosecutor General, Ghorban-Ali Dorri-Najafabadi, confirmed physical abuses in the Kahrizak prison, terming them as "indefensible" and demanding punishment for all those responsible for the prisoners' mistreating.