BAGHDAD, Nov 16 (Reuters) - An Iraqi student who said he was held with prisoners in an Interior Ministry bunker described on Wednesday how he was hung blindfolded in excruciating positions and called a "Sunni dog" by his Shi'ite interrogators.

He was speaking after more than 170 detainees were discovered in the bunker on Sunday night during a raid by U.S. troops who were searching for a missing teenage boy.

"They blindfolded me and tied my hands behind my back and then hung me by a ceiling hook. My shoulders and arms felt like they would come off," the former detainee, who asked to be identified only by his initials, M.I., told Reuters.

"Other times we had to stand up straight and not move for 10 straight hours or face more torture."

There was no way to independently verify M.I.'s account.

The prisoners were found locked in an underground cell near an Interior Ministry compound in the Baghdad district of Jadriya and many of them showed signs of severe hunger, beatings and torture, Iraqi officials and U.S. military sources said.

Prime Minister Ibrahim al-Jaafari said on Tuesday his government was investigating the allegations of abuse.

The discovery of the detainees is embarrassing for the U.S.-backed government, which has promised to deliver human rights after decades of dictatorship under Saddam Hussein.

Iraq's Sunni Arab minority has accused militias linked to the Shi'ite-run Interior Ministry and Shi'ite political parties of rounding up Sunnis in raids and holding them without charge. The Shi'ite-led government has denied the accusations.

LONG ORDEAL

M.I., a Sunni, said his ordeal began one night in late August, when Interior Ministry forces showed up in police vehicles outside his family's house and detained him without charge along with his brother and cousin.

"About forty minutes later I was in a room in a bunker with about 100 others. They blindfolded me and tied my hands behind my back," said the 22-year-old law student.

Interrogators asked him for information on Sunni insurgents in his neighbourhood.

"I didn't know anybody. They hung me from my bound hands from a ceiling hook and whipped me with metal cables. They called us Sunni dogs and thieves or friends of Saddam Hussein.

"They put me in a small cell at first where there were bloody clothes from another prisoner. Then I was in a room with about 100 others. Sometimes they used drills on people."

The bunker scandal is likely to deepen sectarian tensions in Iraq, where Sunnis are waging a bloody insurgency against the Shi'ite-led government.

M.I. said air conditioners were kept at full blast in the bunker, a former bomb shelter located near a building guards said was once a small palace for one of Saddam's daughters.

"They put me in a barrel full of cold water during questioning," said M.I. "They also electrocuted me."

Each prisoner was given half a loaf of bread on a typical day and allowed access to the toilet every two days, he said.

"We would rush to the toilet and drink from the tap because sometimes they would only give us water in soda bottle caps three times a day," he said.

After intensive torture during the first four days by men whom M.I. described as agents from the office of special investigations, inmates were abused less frequently.

But he said life was so tough that prisoners prayed for a transfer to the notorious U.S.-run Abu Ghraib prison, where the scandal of U.S. troops abusing Iraqi prisoners broke last year.

Thin and soft spoken, M.I. sat in the office of a Sunni party on Wednesday, still surprised he was freed six weeks ago.

"We were suddenly taken to meet an official in a jacket and tie. He asked for our names then set five of us free. Others were sent back. No reason was given," he said.