(CNSNews.com) - The Obama administration was aware of ISIS three years ago, when Janet Napolitano was ending her tenure as Homeland Security Secretary, but the group was not the main topic of conversation, Napolitano told MSNBC's "Morning Joe" on Monday.
"Yes, they were on everybody's radar screen. They were there," she said. "But were they the dominant source of conversation? Not at the time, no."
Napolitano said the group has "grown exponentially" in the past three years "in terms of size and capacity and capability." But even three years ago, there were concerns about Americans and Europeans going to Syria to fight with the terrorists, she said.
Napolitano said it's difficult to track the travel of Westerners who may slip into Syria and Iraq from other countries in the region, particularly from Turkey.
"Obviously eyes and ears are attuned to Americans who may be taveling into the region, trying to track travel with the travel documents that DHS does collect. But it's a very big region and these are very big borders, and freedom of travel is freedom of travel, so I would be surprised if you could say, yeah, we have 100 percent control" over who is coming and going.