The former commander of the US military’s highest security prison in Iraq has been detained on suspicion of “aiding the enemy”, having an affair with his female translator and fraternising with the daughter of a prisoner.

Lieutenant-Colonel William Steele was also charged with keeping pornography and classified material in his private quarters, officials said. Before his arrest he was in charge of Camp Cropper prison at the US military headquarters at Baghdad airport.

The charges, revealed today, are another damaging blow to the reputation of the US military prison system, already deeply stained by the Abu Ghraib prison scandal. Camp Cropper contains many inmates formerly held at Abu Ghraib, where US guards tortured and humiliated Iraqi detainees.

Lieutenant-Colonel Steele is being held at a US military detention facility in Kuwait, pending a hearing into whether he should be court-martialled.

The most serious charges of aiding the enemy stem from allegations that he provided “an unmonitored cellular phone to detainees”, officials said. Camp Cropper contains some of Iraq’s most dangerous prisoners, including al-Qaeda terrorists and members of al-Mahdi Army Shia militia. The Times revealed this month that the extremists held there are allowed to run their own prison blocks, which they have turned into centres for recruiting, indoctrinating and training right under the Americans’ noses.

The accusations against the senior officer cover a 17-month period, beginning in October 2005 and ending in February this year. Saddam Hussein was often held in Camp Cropper during that period while being tried for ordering the killing of 148 Shia men in the 1980s.

Lieutenant-Colonel Steele also faces accusations that he “knowingly and wrongfully fraternised with the daughter of a detainee, wherein such acts constituted conduct unbecoming an officer in the Armed Forces”. He is also accused of having conducted an “improper relationship” with his translator. The woman’s nationality was not revealed. While some US military translators are brought in from countries such as Kuwait, Sudan or Egypt, others are Americans who have either studied Arabic or are of Arab origin. The military also uses Iraqi interpreters.

The former camp commander was also said to have provided his translator with special privileges.

The scandal is just the latest embarrassment for the US military, still struggling with the fall-out of the Abu Ghraib prison abuses images released exactly three years ago, which convinced many Iraqis that America was a hostile occupation force. In those pictures naked Iraqi detainees were shown being forced to simulate sexual acts, covered in excrement and being threatened by dogs. One picture showed a smiling US guard giving a thumbs-up next to the corpse of prisoner.

Meanwhile, violence across Iraq continued to defy an American troops escalation. At least 29 people were killed in a series of bombings and shooting, including nine Iraqi soldiers killed when a suicide car bomber blew his vehicle at a checkpoint in Diyala, a province just north of Baghdad where nine US soldiers were killed in a single truck bombing earlier this week.

In the upmarket neighbourhood of Jadriyah in Baghdad, six civilians were also killed by a car bomb parked near a hotel frequented by Western media. And in Saddam’s hometown of Tikrit, the sister-in-law and niece of the dictator’s henchman Ali Hassan Majid al-Tikriti, commonly known as Chemical Ali, were shot dead by unknown gunmen.

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