"Now that negotiations are supposed to be held, why are you setting deadlines and giving ultimatums?" Rafsanjani asked in a Friday prayers sermon carried live on state radio.
"Iran is ready to go there and talk — say whatever you have to say there," said the pragmatic former president who currently heads two of Iran's top clerical and arbitration bodies in Iran.
"Do not try to find fault. Be patient and let wise people sit down and talk to resolve this issue in the negotiations which have started," Rafsanjani added, addressing world powers.
Iran is under a two-week deadline to give a final answer to world powers seeking a breakthrough in the nuclear crisis, after Saturday talks in Geneva with EU foreign policy chief Javier Solana ended in stalemate.
Britain, China, France, Germany, Russia and the United States have offered to start pre-negotiations during which Iran would add no more uranium-enriching centrifuges and in return face no further sanctions.
The United States, which took the unprecedented step of sending a top diplomat to meet Iran's chief negotiator at Geneva talks, has warned Tehran of "punitive measures" if it spurns the offer and presses on with enrichment work.
Iran is already under three sets of UN Security Council sanctions over its refusal to halt sensitive uranium enrichment which the West fears could be aimed at making nuclear weapons.
Iranian officials have repeatedly said they have no intention of freezing enrichment.
Tehran denies allegations that it wants an atomic weapon, insisting that it wants to enrich uranium only to make nuclear fuel.
