The Islamic State group has lost its final sliver of territory in Syria, the U.S.-backed Syrian Democratic Forces said Saturday in declaring victory over the extremists.

However, the announcement came with warnings that the group remains a threat.

Mustafa Bali, a spokesman for the SDF, tweeted that the militant group, also known as ISIS, suffered "100 percent territorial defeat." He said that the eastern Syrian village of Baghouz, where jihadists had been mounting a last stand, "is free and the military victory against Daesh has been achieved." Daesh is ISIS' Arabic acronym.

Bali said that the self-declared caliphate that ISIS established in 2014, and which once sprawled across much of Syria and neighboring Iraq while imposing a brutal rule on as many as 8 million people, had been eradicated. He said the SDF pledged to continue the fight against remnants of the extremist group until they are completely gone.

Saturday's announcement is significant. It marks the end of a 4½-year military campaign by an array of forces against the extremist group, which at its height in 2014 ruled an area the size of the United Kingdom, including several major cities and towns.

It follows remarks by President Donald Trump after landing in Palm Beach, Florida, on Wednesday.

"That’s what we have right now," he said while showing reporters a map comparing ISIS-held territory in Syria and Iraq in 2014 with today. The map indicated ISIS' diminished territory.

It "will be gone by tonight," he said.

On Saturday, the White House issued a statement from Trump announcing that the ISIS-controlled area had been liberated.

"ISIS’s loss of territory is further evidence of its false narrative, which tries to legitimize a record of savagery that includes brutal executions, the exploitation of children as soldiers, and the sexual abuse and murder of women and children," Trump said in the statement. "To all of the young people on the internet believing in ISIS’s Propaganda, you will be dead if you join. Think instead about having a great life."

But the jihadist group remains a serious threat despite repeated announcements from Trump that it had been completely defeated and that its demise meant there was no longer any reason to keep U.S. troops deployed in Syria.

While ISIS has yielded all of its physical territory in Syria or Iraq, it is still a potent fighting force and continues to carry out insurgent attacks in both countries. It also maintains affiliates in Egypt’s Sinai Peninsula, Afghanistan and elsewhere.

ISIS is still "a great threat to our region and our world," said Gen. Mazloum Kobani, the commander of SDF forces. His comments were echoed by William Roebuck, the U.S.'s special envoy for Syria, who said ISIS remains a threat to the U.S. and its allies.

"We cannot be complacent. Even without territory, Daesh and its poisonous ideology will continue to pose a threat to the people of Iraq and Syria, as well as to the wider world. The international community must remain firm in its determination to counter and defeat it," said Britain's foreign secretary, Jeremy Hunt, in a statement.

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According to a study by the Center for Strategic and International Studies, ISIS' military capabilities are far from obliterated. The Washington-based think tank estimates the militant group may still have 20,000 to 30,000 active fighters in Syria and Iraq.

Army Gen. Joseph Votel, commander for U.S. operations in South Asia and the Middle East, said in February that coalition forces needed to maintain "a vigilant offensive against the now largely dispersed and disaggregated (ISIS) that retains leaders, fighters, facilitators, resources and the profane ideology that fuels their efforts."

In January, U.S. military planners and officials issued a report for the Defense Department that said ISIS "could likely resurge in Syria within six to 12 months and regain limited territory" if adequate pressure by coalition forces was not maintained.

After Trump ordered a complete withdrawal of the 2,000 U.S. troops in Syria, Defense Secretary James Mattis announced his intention to resign. In February, under pressure from Congress and the Pentagon, Trump agreed to leave a residual force of about 20 to 400 U.S. troops in Syria for "peacekeeping" purposes.

Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, denied in a statement this week a report in The Wall Street Journal that the U.S. military is now developing plans to keep nearly 1,000 troops in Syria. Dunford called the report "factually incorrect."

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