HRW documented new torture allegations early this year at the Faisaliya prison in northern Iraq, around six months after publishing a report on what it said were "chilling" abuses there and in two nearby facilities.

The rights group said it had reached out about last year's allegations to the Iraqi premier's office, the foreign ministry and the interior ministry, without response.

"If the Iraqi government ignores credible reports of torture, it's no wonder that the abuses persist," said Lama Fakih, HRW's deputy Middle East director.

"What will it take for the authorities to take torture allegations seriously?"

The new reports come from a detainee held in Faisaliya in early 2019.

He described guards beating groups of naked detainees on their feet with plastic piping until they confessed to being affiliated with the Islamic State jihadist group.

The prisoner said guards also waterboarded detainees and suspended them from the ceiling with their hands tied behind their backs.

Faisaliya is located in eastern Mosul, the battered Iraqi city that was IS's de facto capital for three years before security forces recaptured it in late 2017.

Iraq has since tried thousands of its own citizens, as well as hundreds of foreigners, for affiliation to IS.

But rights groups including HRW say the accused are often detained on lofty or circumstantial evidence, their trials do not guarantee due process, and that torture is widespread in Iraq's prison system.

In its Thursday release, HRW said Iraqi judges had "routinely failed" to investigate credible reports of torture in detention.

Earlier this month, it said, Iraq's High Judicial Council told HRW that Iraqi courts had investigated 275 complaints against investigative officers by the end of 2018.

The council said 176 had been "resolved," without providing details of the outcome, while 99 were still being addressed.