In an interview with Human Events on Wednesday, Coats said the "only option" left to prevent Iran from developing nuclear weapons is the threat of military action.
Coats said most Americans agree that Iran must not be allowed to have such weapons, even though Iranian leaders continue to press forward with their nuclear program.
"And yet, no one has gone past that point and said 'If it's unacceptable, what are we going to do?,'" Coats said. "And now it seems we're being asked to accept the unacceptable."
"And the only option now is potential military action if we're going to stop this," he continued. "The unknown factor in all of this is the situation the Israelis are in, sitting there looking at the nation that's proclaiming it wants to eliminate that country from the face of the earth. And that's the kind of threat that I think America has not understood."