(CBS) An assembly line of rotting corpses lined up for burial at Sandy Desert Cemetery is what civil war in Iraq looks like close up.

The bodies are only a fraction of the unidentified bodies sent from Baghdad every few days for mass burial in the southern Shiite city of Kerbala, CBS News chief foreign correspondent Lara Logan reports.

They come from the main morgue that's overflowing, relatives too terrified to claim their dead because most are from Iraq's Sunni minority, murdered by Shiite death squads.

And the morgue itself is believed to be controlled by the same Shiite militia blamed for many of the killings: the Mahdi Army, founded and led by anti-American cleric Moqtada al-Sadr.

The takeover began after the last election in December when Sadr's political faction was given control of the Ministry of Health. The U.S. military has documented how Sadr's Mahdi Army has turned morgues and hospitals into places where death squads operate freely.

The chilling details are spelled out in an intelligence report seen by CBS News. Among some of the details of the report are:

• Hospitals have become command and control centers for the Mahdi Army militia.

• Sunni patients are being murdered; some are dragged from their beds.

• The militia is keeping hostages inside some hospitals, where they are tortured and executed.

• They're using ambulances to transport hostages and illegal weapons, and even to help their fighters escape from U.S. forces.

Iraq's Health Minister, Ali al-Shameri, is a devoted follower of Moqtada al-Sadr. He disputes the report's claims.

"I am ready now, and in the future, to receive investigation teams and journalists to get into any place they want and see whether the Madhi Army are there or not," the Health Minister says. "They will find only doctors, nurses, pharmacy staff and labs and they would find nothing else."

But a hospital worker says Mahdi Army spies are everywhere, and would only talk with both face and voice masked.

"A man was bringing his murdered brother to the morgue. They asked him if he knew who the killers were and he said ‘yes.' They shot him right there," she says.

More than 80 percent of the original doctors and staff where she works are gone, replaced by Shia supporters of the Mahdi Army.

"It's going to get worse because there is no control and no accountability," the hospital worker adds. "No one can stop them. They are terrified... No one will be safe. There will be destruction. Complete destruction is what we are watching with our own eyes, and it's getting worse."

In burial, the victims of Iraq's sectarian slaughter still have no names, only a number on an anonymous grave marker. And with neither the Iraqi government nor the U.S. willing to act, the numbers keep climbing.

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