Ali Bagheri, in an interview with Reuters in Geneva, said Iran needed 20 percent-enriched uranium for its Tehran research reactor and four others being built, and was continuing to convert some of its stockpile into reactor fuel.
"We are waiting for Lady Ashton to call Dr. Jalili, and Dr. Jalili is obviously ready to take the call," Bagheri said.
EU foreign policy chief Catherine Ashton oversees diplomatic contacts with Iran on behalf of the the United States, Russia, China, France, Britain and Germany. Saeed Jalili is Iran's chief negotiator.
"We are waiting to see whether Lady Ashton's response is going to cover the time and venue of another round of negotiations, or will she limit her response to just discussing the substantive side of things," Bagheri said.
In Brussels, a spokesman for Ashton said she had consulted with foreign ministers on how to move forward the process. "Arrangements for a phone call with Dr. Jalili have already been made in order to discuss next steps," Michael Mann said.
The six powers and Iran failed in talks in the Kazakh capital Almaty this month to end the deadlock in a decade-old dispute over Tehran's nuclear program, prolonging a standoff that could yet spiral into a new Middle East war.
At those talks, the six asked Iran to suspend its most sensitive uranium-enrichment work in return for modest relief from international sanctions, an offer Tehran did not accept.
Iran's presidential election is set for June 14, leading to speculation on whether the next round of talks will take place before the poll. "We are ready to continue with the talks ... We have no limits as far as time is concerned," Bagheri said.
Israel, which has long hinted at possible air strikes to deny its arch-foe any means to make a nuclear bomb, suggested this week it would be patient before taking any military action.
Iran says its nuclear work is entirely peaceful and that it is only refining uranium to power a planned network of nuclear energy plants and for medical purposes. Critics accuse it of covertly seeking the means to produce nuclear weapons.