Raad Jamal was 17 when US forces raided his home in the mixed Sunni and Shia district of Doura in June last year. His mother, Suad Ahmed Rashid, who was with him during the interview, told the Guardian: “During the US raid an American officer told my daughter: ‘Tell your brother to confess he is with al-Qaida so we can send him to Camp Bucca [a US prison near Basra] or else we’ll hand him to the Iraqis and they will torture him’.”

Raad and a friend were taken to a US base and were transferred next morning to the seventh brigade of the Iraqi army’s second regiment. Raad said he and his friend were hung from the ceiling on ropes, beaten with electric cables, and taken for interrogation one by one. “They said everyone who comes here has to confess,” Raad said.

He was then sent to another Iraqi army base. “I stayed there about six months. I didn’t confess anything I didn’t do. They write false statements and ask you to press your thumb on it. I refused but they forced my thumb on to the paper,” he said. At the juvenile court Raad encountered a sympathetic judge.

“The judge did not accept my confession. He said I was innocent but for administrative reasons I would have to go to Tobchi until I was released.” He spent a few months in Tobchi and was released in March.

Last year officials from the United Nations Assistance Mission to Iraq (Unami) visited Baghdad’s Tobchi prison, where children awaiting trial are held. They reported that detainees provided “particularly worrisome allegations of ill-treatment or other abuse of juvenile males, several of whom told Unami they had been beaten and sexually abused while held in the custody of the ministries of the interior and defence prior to transfer to a juvenile facility. Upon examining them Unami observed injuries consistent with beatings.”

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.

Kadhim Raouf Ali, deputy director general of Molsa’s juvenile department, told the Guardian that inmate numbers in Tobchi had been sharply reduced this year thanks to speeded-up releases under the new amnesty law. There were only 226 inmates now. But he admitted Karkh was still overcrowded. It was holding 315 children while capacity was 250.

Child detainees in US custody in Iraq fare better than those in Iraqi hands, said Shatha Alobosi, an Iraqi woman MP. Former inmates interviewed by the Guardian confirmed that there is less overcrowding and brutality.

Now, as Iraqi pressure mounts for a return of sovereignty, the US has been moving to release all under-18s. In December last year it held 950 children. The current total is 180.

“We anticipate having less than 100 juveniles in detention by the end of Ramadan [later this month], and hopefully release all juveniles to their families before the end of this year,” First Lieutenant Randi Norton, a US military spokesman, said.

The Iraqi Islamic party, the main Sunni party in parliament, takes a special interest in detainees, adult as well as juvenile, since the majority are Sunnis. It gives aid to poor families who have no breadwinner, and has urged the authorities to improve conditions and release prisoners.

“We still have a long way to go. The problem is how to make a major and drastic reform of the judicial system, and change the mentality of officers in the army and police,” its leader, the Iraqi vice president Tariq al-Hashemi, told the Guardian.

· An Iraqi contributed reporting for this article. Names of inmates and family members have been changed.