U.S. officials

Minister Mevlut Cavusoglu told reporters that Turkish and U.S. military officials had sealed an agreement concerning "the procedures and technical details" of their operations. He didn't provide details, but he has said an extensive, coordinated operation against the militant group would start soon.

"The military authorities have signed off," Cavusoglu said.

Obama's meeting in Ethiopia on Monday comes as an Aug. 17 deadline to reach a deal approaches.

Senior Obama administration officials say if there's no agreement, the U.S. and other nations would deepen pressure on South Sudan's warring factions, possibly through increased sanctions and the pursuit of an arms embargo.