US Secretary of State Hillary Clinton has called on Iran to enter nuclear talks in Geneva next week in good faith.
Mrs Clinton also said that Iran can enrich uranium for civilian purposes in the future, a rare statement for an American official.
She told the BBC that Iran can enrich uranium for civilian purposes at some future date once it has demonstrated it can do so in a responsible manner and in accordance with Iran's international obligations.
"We told them that they are entitled to the peaceful use of civil nuclear energy," Mrs Clinton said.
"But they haven't yet restored the confidence of the international community, to the extent where the international community would feel comfortable allowing them to enrich.
"Iran has to come to the table recognising that they have lost the confidence of even longtime supporters and allies or those who believed them and took them at face value."
The BBC reports Mrs Clinton's words are one of the clearest indications yet that the United States accepts that Iran will one day enrich its own uranium for civilian use.
The Geneva meeting will be led by the EU External Relations chief, Lady Catherine Ashton. The last such talks took place a year ago.