Spillover “is a concern,” said national security advisor Jake Sullivan, with particular worry about the so-called Islamic State, also known as ISIS.

In previous phases of Syria’s long-running civil war, “at its worst, we saw the explosion of ISIS onto the scene,” he said at a conference in Simi Valley, California run by the Reagan National Defense Forum.

The main priority is to ensure “that the fighting in Syria not lead to a resurgence of ISIS,” Sullivan said. “We are going to take steps ourselves, directly and working with the Syrian Democratic Forces, the Kurds, to ensure that does not happen.”

Rebel forces are in the midst of a lightning offensive and say they have begun to encircle Syria’s capital Damascus.

Sullivan said the administration of outgoing US president Joe Biden is working to ensure allies Israel, Jordan, Iraq and others in the region, “who would potentially face spillover effects from Syria, are strong and secure, and we’re in touch with them every day.”

Washington is also alert to stopping a “humanitarian catastrophe, both in terms of civilians, access to life-saving necessities, and in terms of the protection of religious and ethnic minorities in Syria,” Sullivan said.

“Of course, an event like this happens and ISIS immediately looks to take advantage. We have seen reports of ISIS trying… to reconstitute to a certain extent.”

So the US will seek to “contain the potential violence and instability,” protect allies and ensure that ISIS not “get new oxygen out of this” that could lead them to threaten US or allies’ interests, Sullivan added.

Sullivan’s remarks come as Washington prepares for a transition of power next month back to former president Donald Trump, who defeated Biden in November’s election.

Trump, who visited Paris on Saturday, warned against US involvement in Syria, saying the country is “a mess” and “not our friend.”

“THIS IS NOT OUR FIGHT,” Trump said on his Truth Social platform.

Sullivan, addressing Trump’s remarks, agreed, saying “the US is not going to… militarily dive into the middle of a Syrian civil war.”