"This morning we had a combined operation with the Fifth Iraqi Army just south of Baquba and we came upon an al-Qaeda in Iraq prison camp or, if you will, a hideout," the military spokesman told AFP.

"As we came upon this thing, we had the captors or whoever was holding them flee the scene. We immediately secured the area and got the prisoners or those that we rescued to safety," he added.

The camp was holding 41 people, all thought to be Iraqi civilians, many of them showing signs of mistreatment ranging from broken bones and bruises to heat injuries caused by being held with insufficient water, he said.

Some of the prisoners had been held for several months.

"It was evident that they were extremely overjoyed to see us," Donnelly said, adding that the camp had been found after a local tip off, something he saw as a good sign in an area traditionally suspicious of the Americans.

"It is a growing trend that we hope will be sustained, particularly in that part of Diyala, which for us is a very focused effort to secure the population and bring some security to the people in Baquba," he said.

Baquba is the capital of the lawless province of Diyala and part of a belt of violent towns around Baghdad where Sunni insurgents, Shiite militias and security forces are locked in a vicious three-way battle.

al-Qaeda is particularly strong in the area, and has been accused of a number of brutal attacks on local civilians, while it has itself claimed responsibility for the kidnap and murder of dozens of police.

Thousands of US troop reinforcements have flooded into Diyala as part of the broader so-called "surge strategy" to quell fighting in the Baghdad region.