WASHINGTON 

The U.S. will reinforce its position in Syria to protect oil fields from being retaken by the Daesh terror group, a defense official said Thursday. 

Speaking on condition of anonymity, the official recalled that Defense Secretary Mark Esper said he would advise President Donald Trump to "ensure the ongoing success" of efforts to defeat the group in the war-torn country.

The official's remarks came hours after Trump vowed not to allow a "reconstituted" Daesh to take over oil fields in northern Syria.

"The Oil Fields discussed in my speech on Turkey/Kurds yesterday were held by ISIS until the United States took them over with the help of the Kurds. We will NEVER let a reconstituted ISIS have those fields!" Trump said on Twitter, using another name for Daesh.

“One of the most significant gains by the U.S. and our partners in the fight against ISIS was gaining control of oil fields in Eastern Syria -- a crucial source of revenue for ISIS,” said the official.

"The U.S. is committed to reinforcing our position, in coordination with our SDF partners, in northeast Syria with additional military assets to prevent those oil fields from falling back into the hands of ISIS or other destabilizing actors.

"We must deny ISIS this revenue stream to ensure there's no resurgence," the official added.

Another defense official told Anadolu Agency that the Pentagon has yet to determine what types of assets to deploy to the area.

Last week, Trump said he would pull back U.S. troops from northeastern Syria ahead of Turkey's anti-terror operation there, a move which sparked backlash from Capitol Hill.

On Wednesday, Trump said Washington will keep "a small number" of U.S. troops in Syria "where they have the oil."

The president did not specify where the troops would be stationed or how many he is considering but said "we’re going to be protecting" the oil. "And we’ll be deciding what we’re going to do with it in the future.”

*Servet Gunerigok contributed to this story