The military describes the boxes as a humane way of handling violent prisoners, CNN reported. U.S. Marines Maj. Neal Fisher of Task Force 134, the U.S. Marine unit that deals with detainees, said that prisoners in the boxes are observed every 15 minutes and given food and water.

"Someone in a segregation box is actually observed more than those anywhere else," Fisher said. "Their care and custody does not change simply because they are in segregation."

Two photographs of boxes were released in response to a 2005 Freedom of Information Act request from a blogger, CNN said. The smallest boxes are 6 feet by 3 feet by 3 feet and aren't shown in the released pictures.

Jennifer Daskel of Human Rights Watch told CNN she was concerned about whether the boxes are used in extreme heat.