The operation, if approved, would be conducted along with the mostly Kurdish Syrian Democratic Forces militia, a U.S. official says.
U.S. forces have been ordered to prepare to provide security for oil fields in eastern Syria to prevent them from falling into the hands of ISIS, a defense official told NBC News on Thursday.
The possible number of personnel that could be involved at oil fields in the Deir ez-Zor region hadn't been determined, but "we're not talking thousands," the official said on condition of anonymity.
The operation, if approved, would be conducted alongside the mostly Kurdish Syrian Democratic Forces militia, the official said.
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A senior defense official separately told NBC News that President Donald Trump was briefed by Defense Secretary Mark Esper and Army Gen. Mark Milley, chairman of the Joint Chiefs of Staff, on the importance of securing the oil fields so they can't be seized and used to fund ISIS' terrorist activities.
The official said Marine Gen. Kenneth McKenzie, the head of U.S. Central Command, was being given a number of options, among them sending tanks to the region, deploying forces from an armored brigade and using air assets to support ground forces.
Trump signaled the possible action in an address from the White House on Wednesday, when he said "we're going to be protecting" Syrian oil fields.
"We have secured the oil, and, therefore, a small number of U.S. troops will remain in the area where they have the oil," he said.
The United States announced earlier this month that it would withdraw its forces from northern Syria. The move was seen as a major blow to the Kurdish-led Syrian Democratic Forces, or SDF.
Turkey and the United States are NATO allies, while the Kurds have been crucial U.S. allies in the war against ISIS.
But Turkey considers the Kurdish forces to be an enemy, and soon after the U.S. announcement, it began an offensive inside Syria against the Kurdish militants, leading critics to accuse the United States of having abandoned its longtime partner.