The official, who spoke Monday on condition of anonymity, also said that U.S. intelligence analysts believe a video released over the weekend showing the usually reclusive ISIS leader Abu Bakr al-Baghdadi at a mosque in Mosul was authentic.

ISIS fighters have made no real progress in last week or so, with Iraqi government forces holding their ground and even launching counteroffensives, mainly in and around Tikrit, according to the official.

ISIS, which has declared an Islamic “caliphate” extending from northern Iraq into Syria, has been aided by some Sunni tribal and insurgent in Iraq, the official said. But the forces are not conducting joint operations, and are mainly operating “in tandem” and making sure they are not duplicating one another.