Houthis are holding as many as 500 detainees in a prison in southwestern Yemen, a Geneva-based human rights group has said.

The SAM rights groups, in its report published on Monday, uncovered the mistreatment of prisoners at the hands of the rebel group in Salih city of Taiz region.

The Houthis, who control most of the Taiz governorate, have imposed a blockade in the region, causing a humanitarian crisis due to difficulties in the movement to other parts of the war-torn country, and access to healthcare.

The rights group said it documented testimonies from 27 prisoners and three mediators who entered the facility seeking the release of the inmates.

READ: Aid to Houthi-controlled Yemen to be cut back over risk it can be diverted

Houthis, the report said, were employing against their opponents “several measures to physically and mentally torture” them, which include “electric shocks, beatings, starvation, and depriving them of sunlight and adequate ventilation.”

The report mentioned that “atrocities committed” by the rebels were similar to those practiced in “Tadmur prison in Syria and Bastille of France.”

It revealed that there were a total of 51 secret prisons in Taiz: 29 are managed by the Houthis, nine under the control of government forces, another nine run by outfits supported by the United Arab Emirates on the western coast, and four other private facilities.

The illegal secret lock-ups are set up by conflicting parties to torture and abduct their opponents, the report added.

Houthis have so far not responded to the accusations.

READ: Yemenis still in limbo after almost five years of war

Yemen has been beset by violence and chaos since 2014 when Iran-backed Houthi rebels overran much of the country, including the capital Sanaa.

The crisis escalated in 2015 when a Saudi-led military coalition launched a devastating air campaign aimed at rolling back Houthi territorial gains.

Since then, tens of thousands of Yemenis, including numerous civilians, have been killed in the conflict, whereas over 14 million are at risk of starvation, according to the UN.