As many as 600 US troops will remain in northeast Syria to continue counterterrorism operations against the Islamic State, General Mark Milley, chairman of the Joint Chiefs of Staff, said Sunday.
‘‘There will be less than 1,000 for sure,’’ Milley said, referring to the number present when President Trump ordered their complete withdrawal last month. Trump later was persuaded by national security advisers and congressional supporters, such as Senator Lindsey Graham, Republican of South Carolina, to retain an unspecified number of troops whose mission, the president said, was to ‘‘secure the oil’’ from a takeover by the Syrian government or militants.
Milley, speaking on the ABC News program ‘‘This Week,’’ said the number of troops that would remain was ‘‘probably in the 500-ish frame. Maybe 600.’’ He did not mention Syrian oil, but said that ‘‘there are still ISIS fighters in the region and unless pressure is maintained . . . then there’s a very real possibility that conditions could be set for reemergence of ISIS.’’ ISIS is an alternative term for the Islamic State.
‘‘The footprint will be small, but the objective will remain the same — the enduring defeat of ISIS,’’ Milley said.
Syria’s relatively small oil reserves are concentrated in the northeastern part of the country, currently under the control of US-allied Kurdish-led fighters of the Syrian Democratic Forces. Black market sale of the oil by the SDF, primarily to the Syrian government, helps fund those forces.
A separate US force of about 150 remains in southern Syria, on the Jordanian border.
Trump’s withdrawal announcement came after Turkey last month prepared to launch a cross-border invasion, aided by Syrian rebel forces, into northeastern Syria. The administration later reached an agreement with Ankara to remove both US and Kurdish forces — considered terrorists by Turkey — from an area 75 miles wide and about 20 miles deep along the border to avoid a clash with the Turkish force.
That area has since been occupied by Turkey and its Syrian allies, amid sharp criticism of Trump’s withdrawal decision from both within and outside the administration and reports of human rights abuses as more than 100,000 civilians have fled.
In addition to routing the Syrian Kurdish forces, Turkish President Recep Tayyip Erdogan has said he wants to use the border region to resettle up to two million of the approximately 3.6 million Syrian refugees in Turkey. In a speech Sunday, Erdogan said that 365,000 refugees have already been returned to Syria, most of them to an area along Syria’s northwestern border that Turkish forces have also occupied for the last several years.
Late last week, a Turkish official said that 30,000 Syrians had been returned to the northeastern area vacated under the US-Turkey agreement. But at a briefing for reporters in Washington on Thursday, a senior administration official said that ‘‘we’ve seen no refugees moving in’’ to that area.
Another several hundred miles along northeastern border has also been claimed by Russia and Turkey, under an agreement Erdogan struck last month with Russian President Vladimir Putin. Russia is the leading ally of Syrian President Bashar al-Assad.
Erdogan is scheduled to visit the White House this week to discuss with Trump the border area and US-Turkish relations, which have suffered since Erdogan’s decision to buy a Russian air defense system.
Trump’s national security adviser, Robert O'Brien, said Sunday that the United States is still ‘‘very upset’’ by Ankara’s move to buy the Russian S-400 system. Washington says the system is not compatible with NATO forces and could compromise the F-35 fighter jet program and aid Russian intelligence. The Trump administration removed Turkey from the F-35 program in July.
O'Brien told CBS’s ‘‘Face the Nation’’ that if Turkey doesn’t get rid of the Russian system, Turkey is likely to face US sanctions backed by a bipartisan majority in Congress. Trump is scheduled to meet with Erdogan on Wednesday and NATO Secretary-General Jens Stoltenberg on Thursday.
‘‘There’s no place in NATO for the S-400,’’ O'Brien said. ‘‘There’s no place in NATO for significant Russian military purchases. That’s a message that the president will deliver to him very clearly when he’s here in Washington.’’
O'Brien said, however, that the United States will do everything it can to keep Turkey in NATO.
Turkey has been roundly criticized for its incursion into northern Syria to attack Kurdish forces that were fighting with the United States against Islamic State militants. Trump has been denounced for removing US forces from the area before the incursion, but O'Brien said the administration did not pave the way for Erdogan’s offensive into Syria.
Material from the Associated Press was used in this report.