BAGHDAD — The U.N. mission in Iraq expressed "serious concern" Tuesday about overcrowded prisons and the treatment of detainees in Iraqi custody in its latest report on the human rights situation in the country.

The report, which covered the first half of the year, also singled out the problem of so-called honor killings of women in northern and southern Iraq.

Staffan de Mistura, the U.N.'s special representative in Iraq, warned that the issue of detainees will be a major challenge as the United States prepares to turn over control of thousands of inmates in its custody.

The transfer is required under a security pact with the United States that was approved by Iraq's parliament. The agreement still needs to be ratified by the three-member presidential council, which is expected to do so.

"There is no secret that the (Iraqi) prisons are overcrowded and frankly not in very good condition," de Mistura said at a news conference to release the 13th report on the situation of human rights in Iraq.

He cited one example of a prison in which 123 detainees were crammed into a 540-square-foot cell.

Reports of widespread mistreatment and torture of detainees also continue and need more thorough investigation, he said.

"So far we have not seen one case of prosecution," he said.

The U.N. called on the Iraqi government to speed up legal reforms and strengthen the judicial system, saying improvements in the rule of law are necessary to ensure security gains are sustainable.

It also promised to help and said training programs were being held to improve the administration of detention centers as well as the justice system.

"More sovereignty means more responsibility and more responsibility means less impunity," de Mistura said.

The report only covered the six-month period that ended in June due to staffing issues, so the numbers of detainees included was outdated. The U.S. has released thousands since then under an amnesty program.

De Mistura, who heads the U.N. Assistance Mission to Iraq known as UNAMI, estimated Tuesday that there were a total of 40,000 detainees, including some 15,000 being held by the U.S. military.

"UNAMI remains gravely concerned at continuing reports of the widespread and routine torture or ill-treatment of detainees, particularly those being held in pretrial detention facilities, including police stations," the report said.

It also renewed concern about the U.S. detention of suspects for prolonged periods without judicial review of their cases.

Women also faced more violence, including the killing of women for perceived offenses to their families' honor. The problem is of particular concern in the semiautonomous Kurdish region in northern Iraq and in the mainly Shiite southern area of Basra.

A U.S.-Iraqi crackdown against Shiite extremists in Basra has failed to stop the killings, according to the U.N.

De Mistura said 80 to 82 women had reportedly been killed there so far this year, but there has been only one prosecution.

The government has made a more concerted effort to stop the killings in Basra, but the grim statistics show "that the problem needs to be addressed more forcefully," he said.

The U.N. human rights report, which previously was issued quarterly but is now biannual, used to be closely watched for Iraqi civilian casualty figures. That practice stopped when the Iraqi government refused to release the spiraling figures to the U.N.

De Mistura said the situation had improved and he was hopeful casualty figures could be included in the next report.