“I believe strongly that it’s really important for there to be so little enrichment or no enrichment at least for a long period of time because I do think any enrichment will trigger an arms race in the Middle East,” Mrs. Clinton said on CNN in an interview with Fareed Zakaria.

As secretary of state, Mrs. Clinton led the Obama administration’s efforts to get international sanctions imposed on Iran, including its oil sector, in 2012. Mrs. Clinton stepped down in early 2013 and is now considered a top potential presidential candidate for 2016, though she has declined to yet say whether she is running.

Earlier this month, Iran and six world powers, including the U.S., agreed to extend negotiations over Tehran’s nuclear-enrichment program for four more months to reach a comprehensive deal.

Iran agreed to take further measures to curtail the most advanced parts of its nuclear program. It will accelerate the conversion of its 20% enriched uranium into fuel for its research reactor, U.S. officials said. That move will make the material significantly harder to reconvert into a form that can be used for a nuclear weapon, they said.