Less than 1,000 U.S. service members will remain in northern Syria to ensure the lasting defeat of the Daesh/ISIS terror group, U.S. Joint Chiefs Chairman Mark Milley said in remarks aired Sunday. 

Milley told ABC News that the number would be "for sure" less than that level, but he did not specify an exact number other than saying it would likely be around 500 to 600.

"It's in that area," he said on the This Week Sunday morning program. "We're not going to go into specific number because we're still going through the analysis right now."

President Donald Trump has backpedaled on the full withdrawal of U.S. forces he announced in early October, acknowledging some troops will stay in the region "to secure the oil". The Pentagon has maintained that revenues from those natural resources will be given to the SDF, Washington's local ally against Daesh/ISIS in Syria.

Milley maintained, however, in his first television interview since assuming post in September that the U.S. mission in Syria would remain the same.

"There are still ISIS fighters in Syria and unless pressure is maintained on that group then there's a very real possibility that conditions could be set for a re-emergence of ISIS," the Army general said, using another name for Daesh. "The footprint will be small, but the objective will remain the same."

Milley said the death of former Daesh/ISIS leader Abu Bakr al-Baghdadi during a U.S. raid in northern Syria last month will have "a very significant, disruptive effect on the organization as a whole."

"They have apparently replaced him with another leader. We do have a considerable amount of information on that individual, and we'll see in the days ahead, and the weeks ahead, and the months ahead if he's able to piece together his organization or not," he said. "We'll pay close attention to him. And where opportunities arise, we'll go after him as well."