"Because it is not a full dismantling of their program, and that would be historical deal. When you have friends and allies inside the region strongly opposed to it, I would caution," he said on CBS' "Face the Nation."
He noted that the plan does not include a full dismantling of the program, and that the United States should be cautious as a result.
"They are one of the top supporters of terrorism around the world. This is providing them resources and money and we should not take this lightly. We have to have a full dismantling if we want the world to be safer," he said.