Mattis also said, “We’re not just going to walk away right now until the Geneva Process has traction,” and added, “You need to do something about this mess now, not just fight the military part of it and then say good luck on the rest.”

As offensives by Syrian-Russian forces and U.S.-backed units press against remaining pockets of ISIS-held territory, Mattis said the U.S. military’s longer-term objective would be to prevent the return of an “ISIS 2.0.”

He also stressed that longer-term peace efforts are important, and suggested that US forces aim to help set the conditions of a diplomatic solution in Syria, now in its seventh year of civil war.

One key aim for Washington is to limit Iranian influence in Syria and Iraq, which expanded during the war with Islamic State.

Both US President Trump and Russian President Putin asserted that joint efforts will be made to stabilize Syria as its civil war wanes. These would include the expansion of a July 7 truce in the southwestern triangle bordering Israel and Jordan.

Mattis and spoke hopefully about additional areas in the future that might allow for more refugees to return home, said he believed the southwestern zone was working. “You keep broadening them. Try to (demilitarize) one area then (demilitarize) another and just keep it going, try to do the things that will allow people to return to their homes,” he told reporters at the Pentagon. He did not comment specifically about any future zones.

Russia has a long-term military garrison in Syria, but says it wants foreign forces to quit the country eventually.

On Monday, Turkey said on Monday that the United States has 13 bases in Syria and Russia had five. US-backed Syrian YPG Kurdish militia claim that Washington has established seven military bases in areas of northern Syria.

However, the US-led coalition does not discuss the location of its forces.