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By Peter Graff

BAGHDAD, Dec 11 (Reuters) - Iraq will never allow the United States to have permanent military bases on its soil, the government's national security adviser said, calling the issue a "red line" that cannot be crossed.

"We need the United States in our war against terrorism, we need them to guard our border sometimes, we need them for economic support and we need them for diplomatic and political support," Mowaffaq al-Rubaie said.

"But I say one thing, permanent forces or bases in Iraq for any foreign forces is a red line that cannot be accepted by any nationalist Iraqi," he told Dubai-based al Arabiya television.

Rubaie's comments, in an interview first broadcast late on Monday night, were the clearest sign yet that Iraq's leaders are looking ahead to the days when they have full responsibility for the country's defence.

The United States has around 160,000 troops in Iraq, officially under a United Nations mandate enacted after the U.S.-led invasion in 2003.

Iraq formally asked the United Nations on Monday to renew that mandate for a year until the end of 2008. It made clear it would not extend the mandate beyond next year and the mandate could be revoked sooner at Iraq's request.

U.S. President George W. Bush and Iraqi Prime Minister Nuri al-Maliki signed a declaration of principles last month agreeing to friendly long-term ties. Arrangements for U.S. troops to stay beyond next year will be negotiated in early 2008.

Violence in Iraq has fallen in recent months after Bush sent an extra 30,000 troops. Washington intends to reduce its force by more than 20,000 by June 2008 and is expected to decide in March on troop levels beyond that date.

FULLY DEPLOYED

The total number of attacks has fallen 60 percent since June when the additional U.S. troops became fully deployed.

In a statement, the U.S. military said the number of mortar and rocket attacks in Baghdad fell by nearly half last month, to 25 in November from 49 in October.

But U.S. commanders say al Qaeda Sunni Arab militants remain a serious threat, especially in the north of the country.

A suicide car bomb killed one U.S. soldier and wounded two north of Baghdad on Monday, the military said. Nearly 3,900 U.S. troops have been killed in Iraq since 2003.

A suicide car bomb also exploded on Tuesday at a checkpoint in a heavily guarded Baghdad neighbourhood near the homes of former interim Prime Minister Iyad Allawi and the leader of a small Sunni Arab party.

Two people were killed and 12 wounded. Neither politician was at his home and both spend a lot of time abroad.

Allawi's party said two weeks ago it had warned U.S.-led forces and the Iraqi government about threats to kill Allawi, and said its warnings had been ignored.

The head of Iraq's largest mental hospital was killed by gunmen in a drive-by shooting on Monday night, the latest in attacks on medical experts that has caused an exodus of doctors.

U.S. forces detained a suspected Shi'ite militia leader who played a key role training militants how to use weapons such as explosively formed projectiles, a particularly lethal roadside bomb that the military says is made from Iranian components.

The U.S. military said the suspect, who was not identified, was detained along with 10 others in Baghdad on Tuesday. (Additional reporting by Mussab Al-Khairalla, Dean Yates, Aseel Kami and Aws Qusay in Baghdad and Claudia Parsons in New York; Editing by Dean Yates)

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