Secretary of State Hillary Clinton said on "Face the Nation" the United States and its allies would only accept full transparency of the Iranian nuclear system or Iran would face additional sanctions.
"If we don't get the answers that we are expecting and the changes in behavior that we're looking for, then we will work with our partners to move towards sanctions," she said during an interview pre-taped on Friday.
CBS News' Harry Smith, sitting in for Bob Schieffer, asked Secretary Clinton what she meant this summer by "crippling sanctions" which would face Iran should diplomacy fail.
Clinton said that they are still "exploring" how to broaden proposed sanctions and that the current sanctions program is "leaky."
She also noted that multinational discussions on sanctioning North Korea has produced some consensus on how to deal with rogue nations.
On October 1 the five permanent members of the United Nations Security Council - Britain, China, France, Russia and the United States - and Germany will hold talks with representatives of Iran over that nation's nuclear ambitions.
Iran, she said, has present "convincing evidence as to the purpose of their nuclear program. We don't believe that they can present convincing evidence that it's only for peaceful purposes, but we are going to put them to the test on October 1st."
Secretary Clinton said that the only acceptable response from Tehran to ward off additional sanctions would be for Iran to open up its nuclear system to extensive investigation.
"Words are not enough," she said. "They're going to have to come and demonstrate clearly to the international community what they're up to."
Clinton said that it is "hard to accept" that the covert uranium enrichment facility plant disclosed by leaders of Great Britain, France and the United States Friday is for "peaceful purposes," as Iran argues, given that the facility's existence had been hidden from nuclear regulators, thus raising suspicions.
"One has to ask, if it's for peaceful purposes, why was it not public? Why was the fact of it not generally known through our working with partners to discover it?" she asked.
In discussions about Iran, Clinton repeatedly brought up Russia and President Medvedev, who spoke in support of sanctions against Iran Friday, after being informed by President Obama this week about the existence of the previously-secret nuclear facility.
Smith asked the secretary whether Russia is really "in tune" with the United States on this.
Yes, she replied, reiterating that the six countries in talks with Iran are "all in agreement, saying that we expected answers from Iran."
Alluding to Moscow's recent announcement that it would not deploy missiles on its border with Poland after President Obama announced he was killing the Bush-era missile defense system, and Medvedev's criticism of Tehran on Friday, Clinton also said, "in working closely with Russia, sharing information, that they have been quite helpful this past week."