SOUTHWEST ASIA – The number of U.S. troops in Iraq and Syria will go down in response to the recent defeat of the Islamic State (ISIS) in those countries, an official with the U.S.-led military coalition against ISIS said Tuesday.

“Overall in Iraq and Syria, we’re going down,” the official said, who agreed to speak to reporters on the condition of anonymity.

The coalition announced last week it was sending home more than 400 U.S. Marines who were part of an artillery unit that helped local forces retake Raqqa, which was once ISIS’s de facto capital in Syria.

The official said he expected more troops to return home, as the coalition shifts from offensive military operations against ISIS to helping local forces maintain security in the places they have retaken from the terrorist group.

That means fewer troops to enable combat but some to help train local forces on policing and other skills needed to hold territory and maintain security.

Maintaining security in places retaken from ISIS is key to preventing ISIS from returning and unraveling the gains made, the official said. Although many remaining ISIS fighters are taking a last stand in the Middle Euphrates River Valley between Iraq and Syria, some are hiding among the population and are contemplating next steps, the official said.

The number of ISIS fighters in Iraq and Syria is estimated to have shrunk from a peak of 30,000 to 40,000 to an estimated 3,000 currently, the official said.

“The physical caliphate has been destroyed … but I don’t want to confuse this with the ultimate defeat of ISIS. We’re a long way from that,” the official said.

The Pentagon has officially acknowledged the U.S. has 503 troops in Syria and 5,262 in Iraq, per an accounting method for the ISIS war first implemented by the Obama administration.

However, the real number of troops is believed to be hundreds more in both places. As of September 30, there were 1,720 U.S. troops in Syria and 8,892 in Iraq, according to quarterly Pentagon statistics. Defense Secretary Jim Mattis has promised to come up with a more accurate accounting system.

The official declined to say how many U.S.  troops are currently in Syria but insisted the “general trend” is to send them home.

“We don’t have one troop more than is necessary,” the official said.