* More than 400 Sunni Arabs held illegally
* Prison closed down
* Officials deny link to prime minister
BAGHDAD, April 23 (Reuters) - Iraqi authorities have closed down a secret prison where over 400 mainly Sunni prisoners were held without trial, and arrested three officers of the military unit that ran it, an official said on Friday.
The unit that operated the detention centre reported directly to the office of Prime Minister Nuri al-Maliki, a Shi'ite Muslim, but officials denied any connection to or knowledge of the facility in Maliki's inner circle.
"The three officers were detained for interrogation," Kamil Ameen, a spokesman for Iraq's human rights ministry, told Reuters. "What matters to us is that the prison has been closed and it is now part of the past."
The closure of the secret jail comes at a sensitive time for Maliki, who is fighting to hold onto his position as prime minister following an inconclusive general election in March.
A cross-sectarian alliance backed by Iraq's Sunni Arab minority won the largest number of seats, though Maliki's bloc came a close second. Neither has enough seats to form a majority government.
Sunni Arabs dominated under Saddam Hussein and their frustration at the ascendency of Shi'ite political groups -- many with the close ties to Iran -- helped fuel a fierce insurgency after the U.S.-led invasion of 2003.
The sectarian bloodshed that followed was exacerbated in 2005 by revelations that Sunni Arabs had been detained and abused at clandestine jails.
The prison, located at the Muthanna airfield in central Baghdad, held suspected insurgents captured during a military campaign in the northern province of Nineveh last year.
The prisoners should have been handed over to the Justice Ministry for trial but were not.
The Human Rights Ministry said it sent investigators to the facility when it found out about it a few weeks ago and that the detainees there complained they were abused and not allowed to contact their families or seek legal assistance. According to the Los Angeles Times, some prisoners say they were raped.
"There were 431 detainees, 100 of them were released, 20 of them were sent back to Mosul... and the rest were sent to Justice Ministry prisons," Ameen said, referring to the main city in Nineveh.
WARRANTS BEHIND ARRESTS
Military officials said they had warrants for the arrest of all the detainees held at the facility.
"It is not a secret prison, but is a detention cell which is open to all human rights organisations and the Human Rights Ministry," Baghdad's security spokesman, Maj. Gen. Qassim al-Moussawi, told Reuters earlier this week.
"I deny the existence of any secret prison under the authority of the (government) or... of any security force linked to the prime minister." Human Rights Minister Wijdan Salim said in a recent televised discussion that he did not believe there were any other extrajudicial detention centres in Iraq.
A U.S. embassy spokesman said the embassy had raised concerns with senior Iraqi officials over reports of the extrajudicial detention facility and allegations of abuse.
Seven years after Saddam's ouster, about 100,000 U.S. troops remain in Iraq. The U.S. military plans to cut that number to 50,000 by the end of August and for all troops withdraw by the end of 2011. (Additional reporting by Muhanad Mohammed and Aseel Kami; Writing by Nick Carey and Michael Christie, editing by Lin Noueihed)
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