Washington (CNN) President Donald Trump declared Thursday that US backed forces have retaken 100% of the territory once claimed by ISIS in Syria, an announcement that surprised US officials and regional allies leading the fight who told CNN the battle isn't over.

"We just took over you know you kept hearing it was 90%, 92%, the caliphate in Syria, now it's 100%, we just took over 100% caliphate, that means the area of the land we're just have 100% so that's good," Trump said while addressing US troops at Joint Base Elmendorf-Richardson in Alaska on his return trip from Hanoi.

But an official with the Syrian Democratic Forces told CNN's Ben Wedeman the fighting is ongoing and that they were "surprised by this statement" from Trump.

The official also noted that more than a thousand civilians have left the last ISIS enclave within the last few hours.

Multiple US officials told CNN's Barbara Starr that civilians still remain in the last piece of territory remaining under ISIS control.

Trump's comments Thursday followed his December announcement that the US would withdraw US troops from Syria, a decision that has been met with stark opposition from military and intelligence officials who say they were not consulted on the matter.

In December, Trump tweeted, "We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency," later releasing a video where he said US troops are "all coming back, and they're coming back now."

The decision prompted the then Defense Secretary James Mattis to resign from his post the following day.

While Mattis' resignation letter to the President did not explicitly cite his opposition to removing US troops from Syria, the retired four-star general was privately adamant in urging Trump against the pullback.

Last week CNN reported that Trump has agreed to keep about 400 US troops in the country following the withdrawal of most of the troops, according to a senior administration official.

Last month, ISIS claimed responsibility for a deadly explosion in the Syrian city of Manbij that killed four Americans, including two US service members, and at least 10 other people. Prior to that attack, only two US service members had been killed in action in Syria since the start of the campaign in 2014.

Questions around Trump's unexpected decision to remove US military personnel from Syria have continued to swirl in the wake of Mattis' departure despite repeated claims by administration officials, and the President himself, that the terror group has been defeated.

The US commander who has been leading the war against ISIS told CNN's Barbara Starr this month that he disagreed with Trump's decision to withdraw troops and warned that the terror group was far from defeated, in a stark difference of opinion with the President.

Joseph Votel, the top American general in the Middle East, also said that the US-backed forces on the ground in Syria were not ready to handle the threat of ISIS on their own.

"It would not have been my military advice at that particular time ... I would not have made that suggestion, frankly," Votel said of the troop withdrawal announcement. "(The caliphate) still has leaders, still has fighters, it still has facilitators, it still has resources, so our continued military pressure is necessary to continue to go after that network."

Votel, speaking to CNN from Oman earlier this month, revealed he would only have declared that ISIS had been defeated, as Trump did in December, if he was sure they no longer posed a threat.

"When I say, 'we have defeated them,' I want to ensure that means they do not have the capability to plot or direct attacks against the US or our allies," Votel said. "They still have this very powerful ideology, so they can inspire."

Prior to that interview with CNN, Votel had said defeat "doesn't mean the end of the organization."

"Liberation of the terrain that ISIS holds is important, it's an important objective for us to take that away from them. But it doesn't mean the end of the organization," he told reporters while on an official visit to Cairo, Egypt this month.

The commander of US Central Command has also previously said that he "was not consulted" before Trump's controversial announcement late last year that the US would rapidly withdraw its troops from the war-torn country.

And the intelligence community shares similar concerns over the threat ISIS poses.

Director of National Intelligence Dan Coats clearly suggested last month that the intelligence community also believes ISIS remains a threat despite its territorial losses in Iraq and Syria, telling Senate lawmakers this year that the terror group "has returned to its guerrilla warfare roots while continuing to plot attacks and direct its supporters worldwide."

But he also clearly stated that the group maintains a presence in Iraq and Syria.

"ISIS is intent on resurging and still commands thousands of fighters in Iraq and Syria," he said.