National Security Adviser Jake Sullivan said the U.S. was focused on the threat of an ISIS attack on Afghanistan. In an interview on Sunday, Sullivan said he couldn’t give a precise number of Americans remaining in Afghanistan, but said it was believed to be several thousand.

He went on to say the goal was to move people as rapidly and safely as possible. He added the U.S. had the capacity to get large numbers of Americans safe passage to the airport.

Sullivan noted the government was putting the highest priority on stopping or disrupting potential Islamic State attacks.

“Our commanders on the ground have a wide variety of capabilities that they are using to defend the airfield against a potential terrorist attack,” he stated. “We are working hard with our Intelligence community to try to isolate and determine where an attack might come from.”

Sullivan added the military has been working with the Intelligence community to isolate and determine where an attack might come from. This comes as reports mentioned troops have been forced to find alternative routes to the airport and cited the threat of ISIS attacks against Americans and Afghan allies.