BAGHDAD — When the militants of the Islamic State entered the Sunni Arab area of Al Alam, they gave its tribal leaders a message of reconciliation: We are here to defend you and all the Sunnis, they said, so join us.

But after a group of angry residents sneaked out one night, burned the jihadists’ black banners and raised Iraqi flags, the response was swift.

“They started blowing up the houses of tribal leaders and those who were in the security forces,” Laith al-Jubouri, a local official, said. Since then, the jihadists have demolished dozens of homes and kidnapped more than 100 residents, he said. The captives’ fates remain unknown.

In the Islamic State’s rapid consolidation of the Sunni parts of Iraq and Syria, the jihadists have used a double-pronged strategy to gain the obedience of Sunni tribes. While using their abundant cash and arms to entice tribal leaders to join their self-declared caliphate, the jihadists have also eliminated potential foes, hunting down soldiers, police officers, government officials and anyone who once cooperated with the United States as it battled Al Qaeda in Iraq.