June 23 (Reuters) - The U.S. military will hand over security responsibility in Iraq's Anbar province to Iraqi forces on Saturday. Here are facts about Anbar:

** Anbar is an overwhelmingly Sunni Arab region in the west of Iraq that borders Syria, Jordan and Saudi Arabia. Its capital is Ramadi. The Euphrates River flows through the largely desert province. It will be the first Sunni Arab province to be transferred to Iraqi security control. All other provinces handed back so far have been largely Shi'ite or Kurdish.

** Anbar was once the heartland of the Sunni Arab insurgency against U.S. forces and successive Shi'ite-led administrations that took over in Baghdad following the downfall of Saddam Hussein, who was from Iraq's minority Sunni Arab community.

It was once the most dangerous province for U.S. forces. In November 2004, 89 U.S. troops were killed in combat in Anbar. That was at a time when U.S. Marines were battling insurgents for control of the Anbar city of Falluja. In October 2005, 43 troops were killed. Last month, the number killed in combat had fallen to five, including four killed in a single incident.

** Sunni Arab al Qaeda militants found Anbar to be fertile ground and once controlled swaths of the province. But in late 2006, Sunni Arab tribal leaders sick of al Qaeda's indiscriminate killing of civilians and harsh interpretation of Islam joined with the U.S. military to expel the group. That model of security cooperation was replicated elsewhere, especially in and around Baghdad, and has been a key factor in falls in violence. Anbar is now one of Iraq's safest provinces.

** The leader of the Sunni Arab tribal movement that opposed al Qaeda in Anbar, Sheikh Abdul Sattar Abu Risha, was killed in a roadside bomb blast last September, just days after he had met President George W. Bush at an airbase in the province. Bush noted on that trip that he had been told by his military commanders a year before that the province had been lost to insurgents.

** While Anbar makes up nearly a third of Iraq's territory, it has little in the way of proven oil reserves. Most oil wells are in the Shi'ite south and the Kurdish north. This has made Sunni Arab politicians suspicious of any moves to give too much power to Iraq's provinces, fearful that Sunni Arabs will miss out on oil revenues. The Shi'ite-led government has been distributing oil revenue to Anbar in the absence of a national oil law that would divide up the country's oil wealth. (Writing by Dean Yates, Editing by Dominic Evans)

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