US Defense Secretary Robert Gates said on Sunday that Iran is not on the threshold of producing a nuclear weapon and that its program was progressing slower than Tehran expected. "I'd just say, and it's our judgment here, they are not nuclear capable," Gates said in an interview. Speaking to NBC's "Meet the Press," Gates said that Iran was "continuing to make progress" in a nuclear program that Washington suspects is a clandestine effort to develop an atomic arsenal. "It's going slower... than they anticipated. But they are moving in that direction," he said. Asked to compare the danger posed by Iran armed with an atomic bomb or with the ability to produce one, Gates said: "How far have they gone? If their policy is to go (to) the threshold, but not assemble a nuclear weapon, how do you tell that they have not assembled?