Reuters decided to go public on Tuesday, even though its journalists informed the agency in January they were detained for three days in a base near Falluja.
The decision to publish came after the US military insisted there was no evidence to back up the abuse charges.
Two of the Iraqis were forced to lick their finger after inserting it in their anus, while all three said they were humiliated and photographed during their ordeal.
“They said they did not want to give details publicly earlier because of the degrading nature of the abuse,” said Reuters.
Cameraman Salim Uraibi, freelance journalist Ahmad Muhammad Husayn al-Badrani and driver Sattar Jabar al-Badrani were arrested on 2 January as they were covering the downing of a US helicopter near Falluja, west of Baghdad.
They were released without charge three days later.
Uraibi said soldiers told him they wanted to have sex with him and that he feared being raped during his detention.
Reuters said it wrote to the US commander of ground forces in Iraq, Lieutenant General Ricardo Sanchez, to request the inquiry.
Iraqi journalists have often
The general replied the inquiry had been “thorough and objective”, although the three Reuters employees had not been questioned.
The agency has since asked the Pentagon for a review of the findings, but has received no response.
“When I saw the Abu Ghraib photographs, I wept,” Uraibi said on Tuesday. “I saw they had suffered like we had.”
The army in a report found “the detainees were purposefully and carefully put under stress, to include sleep deprivation, in order to facilitate interrogation; they were not tortured”.
But senior Reuters manager David Schlesinger wrote a letter of protest to the Pentagon.
The army’s findings “without even interviewing the alleged victims, along with other inaccuracies and inconsistencies in the report, speaks volumes about the seriousness with which the US government is taking this issue,” he said.
Meanwhile, lawmakers in Washington are urging the administration to hand over control of military prisons quickly to a new Baghdad government.
But Deputy Defence Secretary Paul Wolfowitz and Deputy Secretary of State Richard Armitage said there was no timetable for transfer of the prisons, where abuse and sexual humiliation by US forces have sparked international outrage.