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. "Not yet."
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?
"So, it becomes a serious verification question."
The Pentagon chief also denied that the US administration was resigned to Iran becoming a nuclear-armed power.
"We have not... drawn that conclusion at all. And in fact, we're doing everything we can to try and keep Iran from developing nuclear weapons," he said.
Secretary of State Hillary Clinton, who appeared along with Gates on television political talk shows, argued that Washington's "patience" had helped build international support for sanctions against Iran.
Clinton told NBC that "what we have found over the last months, because of our strategic patience, and our willingness to keep on this issue, is that countries are finally saying, 'You know, I kind of get it... they're the ones who shut the door, and now we have to do something.'"
Clinton and Gates said a new arms control deal with Russia and a revised US nuclear policy would bolster President Barack Obama's diplomatic efforts to isolate Iran and North Korea over their nuclear programs.