A deal on Iran's nuclear programme could be reached within the three- to six-month time frame and would have the potential to dramatically improve the relationship between the two countries, US Secretary of State John Kerry said.
What we need are actions that prove that we and our allies, our friends in the region, can never be threatened by this programme.
"It's possible to have a deal sooner than that depending on how forthcoming and clear Iran is prepared to be," Kerry said in an interview aired on CBS's "60 Minutes" on Sunday.
"If it is a peaceful programme, and we can all see that - the whole world sees that - the relationship with Iran can change dramatically for the better and it can change fast," Kerry said.
He added that Iran could prove its sincerity by immediately opening its nuclear facilities to inspectors and keeping its uranium at lower grades unsuitable for military use.
"Iran needs to take rapid steps, clear and convincing steps, to live up to the international community's requirements regarding nuclear programs, peaceful nuclear programmes," Kerry said.
"Words are not going to replace actions," he said. "What we need are actions that prove that we and our allies, our friends in the region, can never be threatened by this programme."
Iranian President Hassan Rouhani and US President Barack Obama spoke by telephone on Friday in the highest-level contact between the two countries since diplomatic relations were cut a year after the Iranian revolution.
Iran has defended its right to enrich uranium as part of a civilian nuclear energy and medicine programme and denied that it aims to develop atomic weapons, but the United States and its allies have sought an end to higher-grade uranium enrichment that could be a step away from the production of weapons-grade material.
In a separate interview, Iran's Foreign Minister Mohammad Javad Zarif said the country's right to peaceful nuclear enrichment was not for negotiation but stressed that Tehran did not need to enrich uranium to military-grade levels.
"Having an Iran that does not have nuclear weapons, is not just your goal, it's first and foremost our goal," he told ABC's "This Week" programme.
Zarif said Iran was willing to have its facilities visited by international inspectors to prove it was not seeking to build a nuclear bomb.