GENEVA: Tehran on Saturday ruled out freezing its enrichment program, casting doubt over the sense of key nuclear talks between Iran and six world powers.

The talks, with the U.S. in attendance for the first time, had raised expectations of possible compromise on a formula that would have had Iran agree to stop expanding its enrichment activities. In exchange, the six powers, including the five permanent United Nations Security Council members, would hold off on passing new U.N. sanctions against the Islamic Republic.

Iranian Foreign Minister Manouchehr Mottaki said Saturday that forthcoming nuclear talks in Geneva with the participation of a U.S. diplomat for the first time signaled good developments ahead.

The U.S. Undersecretary of State for Political Affairs William Burns will attend the talks in Geneva and join colleagues from other world powers to meet with Iran's chief nuclear negotiator.