Hundreds of children, some as young as nine, are being held in appalling conditions in Baghdad’s prisons, sleeping in sweltering temperatures in overcrowded cells without working fans, no daily access to showers, and subject to frequent sexual abuse by guards, current and former prisoners say.

Daytime temperatures in Baghdad last week averaged 44C (112F). They barely drop below 38C at night. Water supplies in Karkh are spasmodic, and Omar said he was able to shower only once every three days. Boys sleep in four dormitories, averaging 75 inmates in a cell about 5 metres by 10 metres, on double bunks or the concrete floor.

Guards often take boys to a separate room in the prison and rape them, Omar alleged. They also break prison rules by lending their mobile phones to boys to ring home, on condition that each time their families top the phone up by $10 or $20. The teaching staff resigned en masse in November because of low pay, according to an international official. As a result, the children lounge around aimlessly with no daytime activities, other than an exercise yard.

Though the boys in the prison have been convicted, international standards for fair trials are never met. “Trials last on average for 25 minutes, no witnesses are called, confessions are used as the only evidence, and court-appointed defence lawyers get the case file on the day of the trial, leaving no chance to consult the defendant in private,” an international adviser in Baghdad said on condition of anonymity.

The ministry is under Shia control and its forces have repeatedly been accused of targeting innocent Sunnis. Sahar Muhammad, the boys’ mother, told the Guardian that when she was able to visit her sons they told her they were beaten repeatedly in the first days of custody and ordered to sign a blank sheet of paper on which charges would be written later.

The UN found severe overcrowding at Tobchi, with around 400 inmates in a prison with an official capacity of 206. “In some cells juveniles were taking turns to sleep on the floor without mattresses,” the UN reported. The ministry of labour and social affairs (Molsa), which manages the prison, said shortages of funds prevented improvements.