Senior Republican Senator Lindsey Graham, a frequent defender of the president, said a decision by U.S. President Donald Trump to withdraw troops from Syria would be "a mistake".

“An American withdrawal at this time would be a big win for ISIS, Iran, Bashar al Assad of Syria, and Russia. I fear it will lead to devastating consequences for our nation, the region, and throughout the world," Graham said in a statement.

"It will make it more difficult to recruit future partners willing to confront radical Islam. It will also be seen by Iran and other bad actors as a sign of American weakness in the efforts to contain Iranian expansion."

Republican Senator Marco Rubio added that a full, rapid withdrawal of U.S. troops from Syria would be a "grave error" with implications beyond just the fight against the Islamic State.

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The United States is considering a total withdrawal of U.S. forces from Syria as it nears the end of its campaign to retake all of the territory once held by Islamic State, U.S. officials told Reuters on Wednesday.

Such a decision, if confirmed, would upend assumptions about a longer-term U.S. military presence in Syria, which U.S. Defense Secretary Jim Mattis and other senior U.S. officials had advocated to help ensure Islamic State cannot reemerge.

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Still, President Donald Trump has previously expressed a strong desire to bring troops home from Syria when possible.

The timing of the withdrawal was not immediately clear and U.S. officials who spoke to Reuters on condition of anonymity did not disclose details about the deliberations, including who was involved. It was unclear how soon a decision could be announced.