Ali Asghar Soltanieh, Iran's representative to the International Atomic Energy Agency, said Tehran is still studying the proposal and would inform the U.N. nuclear watchdog "next week about our evaluation."
"We are working and elaborating on all the details of this proposal," Soltanieh told state Press TV.
The plan was put forth Wednesday after three days of talks between Iran and world powers in Vienna. The United States, Russia and France endorsed the deal Friday, when an official response from Tehran had been expected.
Iran's acquiescence would be a boost to Obama administration efforts to curtail Tehran's nuclear program and ease Western fears about its potential to make nuclear weapons.
The State Department expressed mild disappointment that Iran withheld a decision and said it was unhappy Iran was not ready to embrace the proposal.
The plan is attractive to the U.S. because it would consume a large amount of Iran's stockpile of low-enriched uranium, thereby limiting the potential for Tehran to secretly convert it into uranium suitable for a nuclear weapon. Iran denies it has any intention of making a weapon, saying its nuclear program is for generating power.
State Department spokesman Ian C. Kelly said the U.S. still hopes Iran will go along with the IAEA option. "This is a real opportunity for Iran to help address some of the real concerns of the international community about its nuclear program and at the same time still provide for the humanitarian needs of the Iranian people," Kelly said. "We hope that they will next week provide a positive response."
Alireza Nader of the RAND Corp. said if Iran rejects the deal, it would "lead to increased tensions" and a possible new set of U.N. sanctions. Nader said the U.N. proposal is "problematic for Iran's hard-line factions."
"Accepting it would indicate a compromise with world powers, and Tehran has repeatedly said it would not compromise," Nader said.
Soltanieh's statement came on the eve of a visit by U.N. nuclear experts to Iran to inspect a recently disclosed uranium enrichment facility near the holy city of Qom. The visit, which kicks off late Saturday, is an indication that Tehran is making good on some of its promises to the West.
The IAEA said Friday that Iran told agency chief Mohamed ElBaradei it is "considering the (U.N.) proposal in depth and in a favorable light, but needs time until the middle of next week to provide a response."
Just hours earlier, Iranian state TV quoted an unidentified official close to the Iranian nuclear negotiating team as saying that Tehran wants to buy nuclear fuel it needs for a research reactor, rather than accept the U.N. plan.
The TV quoted the official as saying Tehran was waiting for a response from world powers to its own proposal to buy the 20 percent-enriched uranium it needs for its Tehran reactor that produces medical isotopes. The U.S.-built reactor has been producing medical isotopes for more than three decades.
While the TV report was not an outright rejection of the U.N. proposal, it raised concerns since Iran has often used counterproposals as a way to draw out nuclear talks with the West. On Thursday, deputy speaker of the parliament Mohammad Reza Bahonar dismissed the U.N. plan.
