"We are more than willing to reach out to the Iranians to discuss a range of issues" if Tehran reciprocates, Hillary Clinton told U.S. lawmakers.
"We are also laying the groundwork for the kind of very tough sanctions, I think you said crippling sanctions, that might be necessary in the event that our offers are either rejected or the process is inconclusive or unsuccessful," she said.
U.S. President Barack Obama said in March that he expected steady progress in relations with Iran.
Iran is under three sets of relatively mild sanctions over its nuclear program, which it insists is purely civilian, but which Western powers, in particular United States, along with Israel, suspect is aimed at developing nuclear weapons.
The most recent UN Security Council resolution on Iran was passed in September last year. Although it omitted new sanctions, due to resistance from Russia and China, it called on Iran to fulfill its responsibilities under previous resolutions, and its commitments to the IAEA.
