(CNN) - ISIS will claim victory over the US and is likely to regain territory as a result of President Donald Trump's decision to withdraw from Syria, according to a new report released Monday by the Pentagon's Inspector General.
"ISIS may conduct opportunistic attacks on US personnel as they withdraw but will leverage the event as a 'victory' in its media," the report said, citing information obtained from US Central Command, which oversees US military operations in the region.
The report, the first of its kind since Trump announced plans to pull all troops from Syria, also says "ISIS remains an active insurgent group in both Iraq and Syria."
"ISIS is regenerating key functions and capabilities more quickly in Iraq than in Syria, but absent sustained [counterterrorism] pressure, ISIS could likely resurge in Syria within six to twelve months and regain limited territory," the report adds.
However, a US official told CNN last week that some military and intelligence officials are concerned an ISIS resurgence could happen even sooner without the US counterterrorism presence.
Trump acknowledged the possibility that ISIS and other terror groups could regain their strength in Syria if he withdraws or reduces troops in those countries and noted that he would send US forces back if they did.
"We'll come back if we have to," Trump said in an interview taped Friday with CBS's Margaret Brennan on "Face the Nation."
"We have very fast airplanes, we have very good cargo planes. We can come back very quickly, and I'm not leaving," he said. "We have a base in Iraq and the base is a fantastic edifice. I mean, I was there recently, and I couldn't believe the money that was spent on these massive runways. And these -- I've rarely seen anything like it."
"They're starting to, as we gain the remainder, the final remainder of the caliphate of the area, they'll be going to our base in Iraq, and ultimately some will be coming home," Trump said when asked when the troops in Syria would be returning.
When Trump announced that US troops would withdraw from Syria in December he declared in a video released on Twitter that "We have won against ISIS. We've beaten them and we've beaten them badly. We've taken back the land and now it's time for our troops to come back home."
But despite ISIS losing nearly all of the territory it once controlled in Iraq and Syria, the Pentagon report, which was published Monday, says "despite the loss of most of its territory in Syria, DoD officials stated that ISIS continues to attract foreign fighters to Syria and Iraq," with the US-led military coalition estimating the number of foreign fighters to be "most likely 50 per month."
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