"Our view is that we are willing to work toward creative outcomes like shipping out the low enriched uranium to be reprocessed outside of Iran but we're not going to wait forever," Clinton said in Jerusalem, where she was holding talks with Israeli officials.
"Patience does have finally its limits and it is time for Iran to fulfill its obligations and responsibilities to the international community and accepting this deal would be a good beginning," she said.
Western powers are awaiting a clear response from Tehran over the nuclear fuel deal brokered by UN atomic watchdog the International Atomic Energy Agency (IAEA).
France has said that under the deal 1,200 kilos of Iranian LEU — enriched at a facility in Natanz in defiance of three sets of UN sanctions — would be shipped abroad for further processing and conversion into fuel for a Tehran research reactor.
Western powers back the deal as the reactor is an internationally supervised facility, and the deal aims at removing Tehran's stock of LEU, a major concern in the West which suspects the enriched material could be further refined for use in nuclear weapons.
Israel, the Middle East's sole if undeclared nuclear power and arch-foe of the Islamic republic, has backed the UN deal.
The IAEA has confirmed that Tehran has given an "initial" response to the deal, but late on Friday the state news agency IRNA reported that Iran's response was "not an answer" to the deal and that it wanted more talks.
On Friday, White House spokesman Robert Gibbs warned that US President Barack Obama will not wait for ever for Iran's formal reply.
"The president's time is not unlimited, this was not about talking for the sake of talking, this was about reaching an agreement that just a few weeks ago seemed to be something that the Iranians wanted," he said.
Iranian lawmakers seem increasingly to be opposed to the deal.
