Female suicide bomber kills Iraq tribal head: police

BAGHDAD (Reuters) - A female suicide bomber killed a prominent Sunni Arab tribal chief who headed a neighborhood security unit and three others in the volatile Iraqi province of Diyala on Monday, police said.

The neighborhood units have been credited for sharp falls in violence across Iraq but have increasingly come under attack by Sunni Islamist al Qaeda because they work with the U.S. military.

Police said the woman went to the home of Thaer Saggban al-Karkhi in Kanaan, southeast of the provincial capital Baquba, knocked on the door and told guards she needed to speak to him.

When Karkhi came to the door she detonated a vest packed with explosives she was wearing hidden underneath her robes, police said. Karkhi's niece was among the dead and two of his bodyguards were wounded.

Al Qaeda, blamed by the U.S. military for most large-scale bombings in Iraq, has increasingly used women wearing suicide vests to carry out strikes after tighter security and protective concrete walls made car bombings more difficult.

Last month, two female bombers killed 99 people in two crowded Baghdad pet markets.

Ethnically and religiously mixed Diyala is one of four provinces north of Baghdad where the U.S. military and Iraqi security forces have launched a series of offensives this year after al Qaeda regrouped in the north.

Al Qaeda and other insurgents were driven out of former strongholds in western Anbar province and in and around Baghdad by security crackdowns last year and the growth of the neighborhood security units.

Such units were pioneered in Anbar in late 2006 after Sunni Arab tribal chiefs turned against al Qaeda because of its indiscriminate killing and its strict interpretation of Islam. The U.S.-backed units have since spread across Iraq.

Attacks have across Iraq have fallen by 60 percent since last June, when an extra 30,000 U.S. troops became fully deployed, with U.S. and Iraqi leaders praising the neighborhood units for their contribution to improved security.

A U.S. military spokesman said on Sunday there were now as many as 90,000 members of such units across Iraq.

(Writing by Paul Tait; Editing by Matthew Jones)