After stunning battlefield advances last month, the extremist Islamic militant group ISIS is now encountering increasing resistance from Iraqi forces and at the same time is quarreling with some Sunni insurgent groups that helped it overrun government-held cities and towns in rapid succession, a senior U.S. counterterrorism official tells NBC News.
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.
The official dismissed reports that the Sunni groups are running the show, saying U.S. intelligence indicates that ISIS, with its small force of about 5,000 "hardened fighters," is the vanguard of the fight against the Iraqi government forces and allied Shiite militias.
As happened in Syria, where ISIS clashed with other Islamic rebels opposed to the regime of Bashir Assad, disagreements have erupted between ISIS and some of the larger Sunni insurgent groups that have been aiding it in Iraq, according to the official.
The official said disputes between ISIS and two large Sunni insurgent groups in Iraq - JRTN, or, in Arabic, "The Army of Men of the Naqshbandi," and "The 1920 Revolutionary Brigades" - led to "skirmishes" between the uneasy allies in the last week.
Those disagreements underline the difficulty building a cohesive fighting force in a country where tribal loyalties often outstrip political and religious alliances to groups like the Ba'athist Party of Saddam Hussein, the official added. The tribal groups do not necessarily follow strict Islamic law the way ISIS does, which naturally leads to conflict, the official added.
Despite the apparent loss of momentum by ISIS, military analysts in Iraq indicate that it remains unclear whether Iraqi forces can regain control of oil fields and refineries, dams, military bases, and the roads to Baghdad.
Also unclear is how much artillery and military hardware the group was able to amass during its run through northern Iraq.
And many analysts in Iraq still expect that ISIS will mount push toward Baghdad at some point, but perhaps only to attempt to surround the city rather than seize it.
Back in Washington, the U.S. official noted that there was surprise within the U.S. intelligence community over the weekend appearance of al-Baghdadi, the ISIS leader, at the Grand Mosque in Mosul.
Baghdadi's appearance, recorded and distributed as a video on jihadi websites, is not something that Osama bin Laden or fugitive Afghan Taliban leader Mullah Omar ever did, though "they never declared a caliphate either," the official noted.
Analysis in the intelligence community suggests that the previously secretive and security conscious al-Baghdadi believes that a caliphate requires the caliph to have a public persona, according to the official.
Will he make regular appearances? The analysts don't know, noting that Mullah Omar was seldom seen in public during his reign as "emir" of Afghanistan, apparently because of security concerns.
Analysts also commented on the significant upgrade in the production values of the ISIS videos in recent months, the official said. The weekend message from al-Baghdadi was not quite up to network quality, but used such editing flourishes as sweeps and dissolves and was a far cry from the crude shots of distant car bomb explosions that were once the hallmark of such communiques, the official said.
Foreign Correspondent Keir Simmons contributed to this report.