“From 2006 to 2008, tribesmen were able to beat Al Qaeda with the cooperation of American forces and the support of the Iraqi government,” said Osama al-Nujaifi, the speaker of Parliament and perhaps the most important Sunni politician in Iraq. “After gaining victory over Al Qaeda, those tribesmen were rewarded with the cutting of their salaries, with assassination and displacement.”

After their success, he said, the Sunni fighters “were left alone in the street facing revenge from Al Qaeda and neglect by the government.”

Sunnis in general have become increasingly bitter toward the government and what they regard as Mr. Maliki’s efforts to push them to the margins of society, with little role in national decisions. In particular, the government’s heavy-handed security strategy, which has often included mass arrests of Sunnis, and the arrest of Sunni leaders on sometimes false terrorism charges, became a rallying point for Sunni protests last year.

As a measure of the polarization between Sunni and Shiite leaders in Iraq, Mr. Nujaifi said he has not even spoken to the prime minister about the crisis in Anbar.

Indeed, many of the tribal leaders say they are happy to accept guns and money from the government to fight the militants, but contend that they are not on the side of the government. They also say they need more supplies from the government, such as winter clothing to fight during the cold desert nights.

“The reason why we returned to carry our weapons and fight is because Qaeda returned to our cities,” said Ahmed Abu Risha, a tribal leader in Anbar who was a critical ally of the Americans.