Iran said on Wednesday that any nuclear fuel swap with the major powers must be based on an agreement it signed with Brazil and Turkey, dismissing reports a revised proposal was on the table.

"If the Vienna group is ready for negotiation over the fuel swap... it would be based only on the framework defined in the Tehran Declaration," Foreign Minister Manouchehr Mottaki told state news agency IRNA.

Mottaki was reacting to reports that the six major powers which have been seeking to allay international concerns over Iran's nuclear programme have been drawing up a new fuel swap deal to replace one proposed last year.

Under the deal drafted in October last year by the UN nuclear watchdog, Iran would have received fuel for a medical research reactor in Tehran from France and Russia in return for shipping out most of its stockpiles of low enriched uranium.

After a prolonged stalemate over the proposal, Brazil and Turkey brokered a modified agreement in May but the United States rejected it, arguing it failed to take into account additional uranium enriched in the meantime and led the Security Council in imposing a fourth package of UN sanctions.

Last month, White House spokesman Robert Gibbs said any new fuel swap deal would be more onerous than the one on the table last year as Iran needed to be accountable for its persistent defiance of Security Council ultimatums to suspend uranium enrichment.

"In order to live up to the responsibilities that they have made and to lift any sanctions, they would have great responsibilities," Gibbs said on October 28.

"The responsibilities get greater each and every day even as the sanctions impact their economy more and more."

Gibbs spoke after the New York Times reported that Washington and its European allies were preparing a new, more onerous offer for Iran than the one proposed last year.

The new offer would require Iran to send more than 4,400 pounds (1,995 kilogrammes) of low enriched uranium out of the country, an increase of more than two-thirds from the amount required under the deal proposed last year.

Iran and the major powers are set to hold fresh nuclear talks later this month after a year-long hiatus. The world powers want the talks to focus on Iran's overall nuclear programme.