The United Arab Emirates currently runs 18 "secret prisons" in Yemen, the French newspaper Le Monde has revealed.
An investigation published by the newspaper stated that the UAE-run prisons contain numerous Yemeni detainees.
A number of Yemeni prisoners, who have been transferred to Saudi Arabia and the UAE, were also interrogated by investigators from the US, according to the newspaper.
The UAE has repeatedly stressed that it had entered Yemen to fight the Houthi militant group, but Le Monde reported that its real goal is to fight the Muslim Brotherhood-affiliated Al-Islah Party.
Abu Dhabi, the newspaper pointed out, supplies the Abu Al-Abbas Shia militia with weapons to fight the Sunni Al-Islah Party in Taiz.
In late June, Human Rights Watch formed a panel to investigate reports about secret prisons in Yemen where inmates have been tortured. The organisation accused the UAE of operating two informal detention facilities in Yemen.
Yemeni jails, in which detainees were reported to have been tortured, are built in military bases, airports and ports.