Iraqi Prime Minister Haider al-Abadi celebrated Sunday with troops in Mosul after forcing Islamic State militants from some of their last strongholds in the city, although fighting continued a few blocks away, Iraqi state TV reported.
“This fight is far from over,” said Jennifer Cafarella, an analyst at the Institute for the Study of War.
The Islamic State, also known as ISIS, has proved capable of plotting terror attacks even as it has lost significant territory. Many of its leaders have already escaped Raqqa, its capital in Syria, and have fled to other strongholds inside the country.
“We’ve consistently been chasing ISIS’ communications node around the battlefield,” Cafarella said.
Still, U.S. officials and analysts say pushing militants out of their major strongholds in Iraq and Syria is a critical first step to an overall defeat of the militant group, which emerged as a worldwide menace three years ago when it swept through parts of Iraq and Syria.
The defeat of ISIS in Mosul also frees thousands of Iraqis from the group’s brutal rule. Al-Abadi said in late June that the militant group's self-proclaimed caliphate was finished and hailed Iraq's seizure of the ruins of the famed al-Nuri mosque as a major victory over ISIS.
Several hundred militants remained in the city, but they were surrounded and losing more territory by the day. In Syria, U.S.-backed local forces have surrounded Raqqa and have begun an assault into the city.
The offensives in Raqqa and Mosul have put the terror group on the run and have forced the group to relinquish much of the territory it controlled at its peak in 2014.
But the group has also proved stubbornly resilient.
Some ISIS leaders have already fled to militant-controlled areas along the Euphrates River Valley south of Raqqa, which have become a key stronghold for the militants now that Mosul and Raqqa are under military pressure.
In Iraq, ISIS fighters still control Tal Afar — a town west of Mosul in northern Iraq —and desert towns in the far reaches of western Iraq.
“There still remains ISIS holdouts in both Iraq and Syria,” said Col. Ryan Dillon, a U.S. military spokesman in Baghdad. “We'll continue to support and stand shoulder to shoulder with our partners in those fights.”
The next stage of the battle in Iraq will be determined by Iraq's government, the Pentagon said. The U.S. military said it would continue to provide advisers, airstrikes and other support for Iraq's military.
“There’s plenty of work left in this country,” said Maj. Gen. Joseph Martin, a top coalition commander in Iraq.
The U.S. military has deployed about 5,500 troops in Iraq to advise and train Iraqi forces and nearly 1,000 troops in Syria to support the Syrian Democratic Forces. The U.S.-led coalition has launched daily airstrikes that have crippled the Islamic State's finances and leadership.
The Pentagon has said that ISIS will likely revert to a more conventional terror organization that operates from caves or other hiding places as it loses territory. But the loss of a caliphate will at minimum take away a key selling point to get recruits from around the world.
The sheer resiliency of the militants have commanders concerned, however. The Islamic State's anti-West ideology continues to appeal to some young people across the Middle East, and the terror group has also capitalized on local grievances to gain support in some areas.
“When I consider how much damage we’ve inflicted, and they’re still operational, they’re still capable of pulling off things like some of these recent terrorist attacks we’ve seen internationally, I think we have to conclude that we do not yet fully appreciate the scale or strength of this phenomenon,” Lt. Gen. Michael Nagata, an official at the National Counterterrorism Center, said in an interview published by the Combating Terrorism Center at West Point.