The White House has ordered the Pentagon to pull U.S. troops from Syria immediately, a U.S. defense official confirmed to CBS News correspondent David Martin.

President Trump, who has long wanted to withdraw troops from the war-torn region, suggested on Twitter Wednesday that the Islamic State of Iraq and Syria (ISIS) is defeated and therefore, there is no reason to be there.

"We have defeated ISIS in Syria, my only reason for being there during the Trump presidency," Mr. Trump tweeted Wednesday morning, without explicitly confirming an order to look to withdraw troops.

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The president expanded on that in a video tweet Wednesday evening.

"We've been fighting for a long time in Syria. I've been president for almost two years, and we've really stepped it up, and 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 home. .... Now we've won. It's time to come back. They're getting ready, you're gonna see them soon. These are great American heroes. These are great heroes of the world. Because they've fought for us, but they've killed ISIS, who hurts the world. And we're proud to have done it. And I'll tell you, they're up there looking down on us and there's nobody happier or more proud of their families to put them in a position where they've done such good for so many people."

But the Pentagon was less definitive on that, and Mr. Trump's own administration has suggested the battle in Syria isn't over. Plus, key senators claimed they weren't briefed on the decision ahead of time, prompting intense criticism even from some of the president's strongest supporters.

"At this time, we continue to work by, with and through our partners in the region," Pentagon spokesman Col. Rob Manning told reporters in a statement.

When reporters asked Deputy Secretary of Defense Pat Shanahan to comment on the reports of troops withdrawing from Syria, he responded, "I'm not going to make any comments."

Rep. Adam Kinzinger, a veteran of the U.S. Air Force who served in Iraq and Afghanistan and now serves on the House Foreign Affairs Committee, said it's "simply not true" ISIS is defeated in Syria.

This is simply not true. https://t.co/Jvie2NxgWz — Adam Kinzinger (@RepKinzinger) December 19, 2018

Two weeks ago, Special Envoy Brett McGurk said the end of ISIS will be a long-term initiative, and "nobody is declaring mission accomplished."

The National Counterterrorism Center's guidance from October suggests that while efforts to contain ISIS have seen substantial successes this year, the terror network remains "an adaptive and dangerous adversary," and in Iraq and Syria, its leaders are relocating to rural safe havens to "support a long-term insurgency." While the ISIS' safe havens in Iraq and Syria have "largely collapsed," it still maintains a robust global enterprise of nearly two dozen branches, each with "hundreds to thousands of members."

Mr. Trump has long expressed a desire to withdraw troops from the war-torn region, but had been urged against rapidly withdrawing U.S. armed forces. Joint Chiefs Chairman Gen. Joseph Dunford told the Washington Post earlier this month that "we still have a long way to go" and was "reluctant to give a fixed time" on troop withdrawal from Syria. The president recently announced that Dunford will be replaced when his term expires in October 2019 by Gen. Mark Milley, the Army chief of staff.

In April, Director of National Intelligence Dan Coats said the administration had made a decision about whether to pull troops, although White House press secretary Sarah Sanders did not say at the time whether that meant troops were coming home.

Reports of the president's intent to withdraw from Syria sparked intense criticism from Trump ally Sen. Lindsey Graham, who said pulling troops would be an "Obama-like mistake" — something Graham knows would insult the president. Vice President Mike Pence briefed senators, who expressed intense frustration over not being briefed before the president made the decision. Some said they learned of the decision from the media.

Graham said he told Pence that, "if Obama had done this all of us would be going nuts...I want hearings as soon as possible to find out, was this decision made based on sound military advice or was it in spite of it?"

Sen. Bob Corker, the Republican chairman of the Senate Foreign Relations Committee, told reporters, "It doesn't feel to me there was any interagency process."

"I felt badly for the vice president because he had talking points and it's just there's no way he could really defend. He did what a loyal soldier would do but it was not resonating," Corker also said.

David Martin, Margaret Brennan, Alan He, Kathryn Watson, Eleanor Watson and Olivia Gazis contributed to this report.

Editor's note: An earlier version of this report said that Gen. Dunford had been replaced by Gen. Mark Milley as Joint Chiefs chairman, but his term does not expire until October 2019.