* Car bombs hit northern Iraq, six dead
* Government asks Kurdish troops to pull back
* U.N. marks fifth anniversary of blast
* 14 U.S. troops dead so far in August, more than July
By Aws Qusay
BAGHDAD, Aug 13 (Reuters) - Bombs in four parts of northern Iraq killed at least six people on Wednesday, and Iraqi forces said they expected more attacks as they pursue Sunni Arab militants in the volatile north.
With violence falling in other parts of Iraq, the ethnically and religiously mixed provinces north of the capital Baghdad remain the most volatile parts of the country.
Al Qaeda Sunni Arab militants driven out of other areas have sought refuge in the fertile river valleys of the north. Tension between Arabs and Kurds has also simmered in cities and villages along the frontier with the Kurdish autonomous region.
In a sign of the ethnic tension, the central government said it had asked ethnic Kurdish forces to withdraw from an area outside their autonomous region. The Kurds said they had not agreed to pull back their troops to Kurdistan.
The U.S. military said a suicide car bomber struck an Iraqi army patrol in the northern city of Mosul, killing an Iraqi soldier, two civilians and wounding 15 people.
A parked car bomb in the town of Qaiyara south of Mosul killed two people and wounded nine. A roadside bomb near Baquba north of Baghdad killed a woman and wounded two.
Another suicide car bomber struck the mayor’s office in the small town of al-Motaqa near the ethnically divided city of Kirkuk on Wednesday. The mayor, Abdul Karim al-Jubouri, who also leads pro-U.S. security volunteer forces in the area, was wounded along with three bodyguards.
Disagreement between Kurds, Arabs and Turkmen over control of Kirkuk has held up a provincial election law, delaying voting throughout the country and paralysing its politics.
A U.S. soldier and an Iraqi interpreter were killed by a roadside bomb in Baghdad. Fourteen U.S. troops have died this month, more than total of 13 for all of July, but still reflecting a dramatic improvement in security from a year ago.
U.S.-backed Iraqi forces are conducting a crackdown in Diyala province north of the capital, which follows operations in and around Mosul — all targeting al Qaeda militants.
"They know very well that this is their last redoubt," Defence Ministry spokesman Major-General Mohammed al-Askari told a news conference, predicting more bombings.
"We expect the battle will be a battle of roadside bombs, explosive belts and a battle of explosions."
On Tuesday, the governor of Diyala province survived an assassination attempt when a suicide bomber struck his convoy in the provincial capital Baquba. A curfew was imposed on the town.
Askari said Iraqi military operations in Diyala would resume on Friday after a four-day pause ordered by the authorities to give militants a chance to surrender.
He also said the central government had told Kurdish troops it was ready to take over security from them in Diyala, and they would soon withdraw to provinces within autonomous Kurdistan.
A brigade of the Kurdish troops, known as Peshmerga, patrols parts of Diyala where many Kurds live, even though the province is not part of Iraq’s Kurdish autonomous region. The Kurdish government said it had not reached an agreement to remove them.
"So far there is no deal made. Talks are going on between the two governments regarding the presence of this brigade in the area," Jaffar Mustafa, Minister for Peshmerga in the Kurdish regional government told Reuters in the Kurdish capital Arbil.
In the capital, the U.N. mission in Iraq held a ceremony to mark five years since a bomb at its Baghdad headquarters killed 23 people, a turning point in 2003 that prompted nearly all aid and development organisations to pull out of the country.
A new U.N. mission is back with an expanding role and signed a deal on Wednesday with Iraq’s planning ministry to do development work for two more years.
"There are moments when we wonder whether all this was worth it or not," U.N. special representative Staffan de Mistura said.
"What we are doing at the moment is sending a signal that the U.N. is back. The U.N. is back to stay. The U.N. is back to have its footprint increasing." (Additional reporting by Waleed Ibrahim, Missy Ryan and Peter Graff in Baghdad, Shamal Aqrawi in Arbil, writing by Peter Graff, editing by David Clarke and Jon Boyle)