Ben Rhodes, the deputy national security adviser to President Barack Obama, told reporters Friday that the U.S. would not be "restricted to borders" in responding to terror threats emerging from the group. He hinted that any long-term strategy to confront ISIS has to "deal with both sides of the border" of Iraq and Syria. 

"When you see somebody killed in such a horrific way, that represents a terrorist attack. That represents a terrorist attack against our country and against an American citizen," Rhodes said in a press conference from Martha's Vineyard, where Obama is vacationing through the weekend.

"If you come after Americans, we're going to come after you wherever you are," he added.