BAGHDAD – More than 11,000 Iraqis have been released from American detention centers this year, leaving nearly 20,000 still in custody, the U.S. military said Saturday.

Some 19,700 Iraqis remain in detention at two main centers in Iraq – Camp Cropper in Baghdad and Camp Bucca in southern Iraq. Several hundred more detainees are expected to be released by mid-September, military spokesman Maj. Neal Fisher said in a statement.

The United States wants to transfer the remaining detainees to Iraqi control, but has been hindered by the lack of adequate Iraqi prison space and trained guards. More than 8,900 people were released from detention last year.

Rights groups have criticized U.S. detention policy as a misrepresentation of international law, which requires some form of legal process to detain someone.

But the U.S. military has said its detention system is authorized by a U.N. resolution under which the Iraqi government allows U.S. troops to arrest people at will.

Fisher said each detainee appears before a review board every four to six months. The military has said the average detention time is 330 days.

Meanwhile, gunmen killed a member of a local U.S.-allied Sunni group and his family north of Baghdad, the U.S. military said Saturday.

The man was killed Friday night in his home in the village of Withah in the volatile Diyala province. His father, mother and an infant were also killed in the attack, which was in coordination with an assault on a nearby Iraqi army checkpoint that wounded one Iraqi soldier, the military said.