The United States could leave a residual military force in Iraq after the Islamic State is pushed out of its last stronghold there, Defense Secretary Ash Carter indicated Tuesday, saying militants loyal to the terror group will continue to pose a significant threat throughout the region well into the future.



Speaking at what's expected to be his final Pentagon press briefing, Carter said U.S. officials are discussing the matter with Iraq's government, which would have to agree to allow U.S. forces to stay — a prospect that makes many Iraqis leery. But, the secretary added, ISIS fighters will remain active after U.S.-backed Iraqi ground forces retake the northern city of Mosul, which has been the focus on a months-long offensive that, by most accounts, is progressing much slower than anticipated.





"It'll take some time to consolidate Iraqi security, even after the fall of Mosul, which will occur — like the defeat of ISIL will occur," Carter said, using another name for the Islamic State. "But there will be other cities and towns in Iraq where the government's control will need to be secured. And there will be an ISIL tendency to go underground and to go to more isolated regions and continue to try to mount operations, and that'll require a sustained effort. And I think the United States and the international coalition, everybody's realistic about that."





Carter referenced a meeting in London last month with his counterparts from several nations supporting operations against the Islamic State in Iraq and Syria, where another offensive has begun targeting the group's self-declared capital in Raqqa. "There wasn't any question in the room," he said, "that ISIL would have a life after Mosul, and that we would all need to continue to be in the business of protecting our people."

Speaking alongside Carter on Tuesday, Joint Chiefs Chairman Gen. Joseph Dunford said the question of whether to retain a "long-term presence in Iraq" will be addressed by President-elect Donald Trump's incoming administration with advice from the general and his commanders.

"It has to be done in conjunction with the Iraqi government," Dunford said.

Officially, there are about 5,500 American troops authorized to operate in Iraq and Syria but the number is believed to be greater when considering personnel there on temporary orders. Personnel are distributed across a range of facilities in Iraq, including in and around Baghdad, and at bases and airfields within striking distance of Mosul. In Syria there are about 500 special operations forces and other specialized advisers whose location and movement is less known.

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U.S. officials have indicated that, once Mosul and Raqqa fall, ISIS is likely to rely more exclusively on guerrilla tactics and that the fight will transition to a counter-insurgency mission with challenges similar to those U.S. forces encountered during their occupation of Iraq throughout much of the last decade.

Many observers believe that once the ISIS caliphate is dismantled, U.S. forces will have no choice but to continue conducting airstrikes and providing allies on the ground with tactical assistance and logistical support.

Marine Corps Col. Bill Vivian, the head of Special Purpose Marine Air-Ground Task Force-Crisis Response-Central Command, and Sgt. Maj. Edward Zapata, the unit's top enlisted leader, conduct a battlefield assessment at a coalition base in northern Iraq on Dec. 26, 2016.

Photo Credit: Lance Cpl. Kyle McNan/Marine Corps

For now, ISIS fighters are well entrenched in both of its remaining strongholds, though Iraqi soldiers and Kurdish forces have retaken some territory in eastern Mosul, officials said last week. American military advisers have at times accompanied Iraqi units into the city.

In Syria, the battlefield is more complex. One variable is the less-experienced, less-organized group of allies U.S. forces are supporting against ISIS there, a patchwork of units known collectively as the Syrian Democratic Forces. Another is the simmering geopolitical tension between the U.S. and its NATO ally Turkey. Turkish ground forces are active in northern Syria, fighting to repel Islamic State fighters from areas around its border. But Washington's support for Syrian Kurdish militias, entities Ankara considers terrorists, has proven divisive.

In November, the U.S. stopped providing the Turks with air support and ground-level military advisers after Turkish commanders launched an offensive on al Bab, a Syrian border town and Islamic State transfer point 125 west of Raqqa, rather than joining efforts to target the main U.S. objective. American officials have sought to downplay the tension and last week said that U.S. warplanes had resumed backing Turkish ground units, conducting show-of-force flights in al Bab. American surveillance flights there also are expected to resume.

There were reports this weekthat Russian military aircraft have, in lieu of U.S. support, begun striking Islamic State targets in al Bab. Dunford said Tuesday that those attacks, which according to the New York Times included unguided munitions, were carried out without coordination between the Russians and the Turks.

"I speak quite frequently with my Turkish counterpart," Dunford said. "He's very open and transparent about the communication that he's had with our [mutual Russian] counterpart. But he's also said that the Turks, at this time, are not cooperating and coordinating, conducting operations in conjunction with the Russians. ... And I'm not aware that those strikes have been anywhere near proximity to Turkish forces or put them at risk either."



Asked about the incoming administration's indications that coalition air operations may intensify in Syria and Iraq, Dunford said that such support will be dictated by demonstrated battlefield gains by U.S. allies on the ground. The risk of causing civilian casualties, which has governed what U.S. forces could target in Afghanistan and previously in Iraq, has "not been the driver of the air campaign" against the Islamic State, he said.

"The pace of our bombing is driven by the pace of operations of our partners," Dunford said. "We're providing air support that's consistent with the progress of the Iraqi security forces in the case of Iraq. ... And the same is true in Syria. The tempo of our air campaign in Syria is directly linked to the pace of operations of the Syrian Democratic Forces that we're supporting.



"The air campaign will accelerate," he added, "as the operations of our partners accelerate."



Andrew deGrandpre is Military Times' senior editor and Pentagon bureau chief. On Twitter: @adegrandpre .