LONDON -- A judge-led inquiry on Wednesday found British soldiers mistreated nine Iraqi detainees after a 2004 battle, but it rejected allegations that soldiers murdered and tortured prisoners.

The inquiry, which began in 2009, concluded that British soldiers used methods such as blindfolding prisoners and depriving them of food and sleep during "tactical questioning" at Camp Abu Naji in southern Iraq. The soldiers also used threatening interrogation techniques that breached the Geneva Convention, the report said.

Thayne Forbes, a former High Court judge, also criticized British soldiers for "tasteless trophies" such as striking poses for photos with detainees.

But he said that allegations that British soldiers had murdered, mutilated and tortured detainees after the May 2004 battle were found to be "entirely the product of deliberate lies, reckless speculation and ingrained hostility."

The report suggested that some of the detainees, described as supporters of the Madhi Army insurgent group, lied about the most serious allegations to discredit British troops.

The inquiry, which heard evidence from hundreds of military personnel and 55 Iraqi witnesses, was ordered in 2009 amid concerns from High Court judges that defence officials had not properly investigated what happened in May 2004.

The drawn-out investigation has cost 25 million pounds (US$39 million) in public funds. Defence Secretary Michael Fallon said the government would try to recoup some of the cost.

"This is 10 years after the incident took place and it cost a huge amount of money, and it was not until very late in the day that the lawyers for the detainees accepted that these allegations weren't true," Fallon said. "Had they accepted that and conceded that much earlier, a great deal of money might have been saved."