Unlikely Allies Aid Militants in Iraq

Radical Sunni Fighters Are Aided by Local Tribes Who Sympathize With Their Goal to Oust Baghdad Government.

Radical Sunni fighters, who seized another northern Iraqi city on Monday, are being aided by local tribes who reject the Islamists’ extreme ideology but sympathize with their goal of ousting the Shiite-led government in Baghdad.

The uneasy alliance helps explain how several hundred insurgents from Islamic State of Iraq and Al Sham, or ISIS, have handily defeated a far larger, better-equipped Iraqi army and come to control about a third of Iraqi territory.

Sunni tribal leaders say mistreatment by the government of Prime Minister Nouri al-Maliki has sparked protests and militancy among their ranks that created fertile ground for the al Qaeda offshoot to emerge victorious.

“This is a revolution against the unfairness and marginalization of the past 11 years,” said Sheikh Khamis Al Dulaimi, a tribal leader in the Anbar Military Council of Tribal Revolutionaries, a group that has led protests against Mr. Maliki for the past year and a half.

Officials from the U.S. and Iran, which both back the Maliki government, signaled Monday a willingness to work together to halt ISIS’s momentum—though with no military coordination, the White House stressed—during talks in Vienna over Tehran’s nuclear program.

President Barack Obama formally notified Congress on Monday that he would send up to 275 U.S. military personnel to Baghdad “to provide support and security for U.S. personnel and the U.S. Embassy in Baghdad.” Mr. Obama last week also said the U.S. was considering other steps, including airstrikes.

The developments came after the insurgents seized the northwestern Iraqi city of Tal Afar, sparking an outflow of residents. The city was being guarded by a U.S.-trained Iraqi commander who had aimed to amass troops there and mount a counteroffensive to reclaim the city of Mosul from the rebels, said Iraqi military officials.

More From The Wall Street Journal (subscription required):