The International Campaign for Human Rights in Iran is demanding an end to “secret mass executions and inhumane conditions” in Vakilabad Prison in Mashhad.

The U.S.-based rights group said in a statement that Iran’s judiciary has made no efforts to rectify the “horrific situation” in Vakilabad Prison, where inmates are subjected to “sardine-like overcrowding, health threats, humiliations and mass executions.”

Hashem Khastar, a Vakilabad prisoner of conscience and a member of the Khorasan Teacher’s Union, has described the prison conditions in a letter addressed to the head of Iran’s judiciary, Ayatollah Amoli Larijani.

The Campaign cites Khastar’s letter in reporting that the prison is currently being run at four times its inmate capacity, and the prisoners are denied the most basic living needs. Comparing Vakilabad to Hitler’s death camps, Khastar reportedly writes that on August 10, 2010, 63 prisoners were executed en masse.

In March, UN Secretary General Ban Ki-moon issued a report expressing concern over the conditions at Vakilabad. The report, which was reviewed by the UN Human Rights Council, noted that Iranian judiciary officials have confirmed only 60 executions at the prison. The Campaign cites reliable reports for its belief that the true numbers are certainly much higher, with at least 300 prisoners secretly executed in Vakilabad Prison in 2010.

Hadi Ghaemi, spokesman for the International Campaign for Human Rights in Iran said: “The conditions at Vakilabad and other prisons need to be on the agenda of the new UN special rapporteur and the High Commissioner for Human Rights.”

The Campaign also calls on the Iranian judiciary “to launch an independent investigation into the outrageous conditions at Vakilabad and other prisons, and to take immediate steps in addressing the urgent crisis unfolding there.”