US Secretary of State Hillary Clinton on Thursday urged Iran to accept unchanged a UN-drafted deal with global powers on its nuclear program.

"As I have said, this is a pivotal moment for Iran, and we urge Iran to accept the agreement as proposed," Clinton told reporters, flanked by new German Foreign Minister Guido Westerwelle.

"We will not alter it, and we will not wait forever," Clinton said.

Iran had been initially due to give its response to the deal by October 23.

The plan calls for Iran to export to Russia more than 2,640 pounds (1,200 kilos) of its 3.5 percent, low-enriched uranium (LEU) for refining up to 20 percent, to fuel a Tehran reactor that makes medical isotopes.

France would then fashion the material into fuel rods for the reactor.

The deal would have the effect of taking substantial uranium supplies out of Iran and leaving the Islamic Republic without sufficient material to make a nuclear weapon, at least from stockpiles known to the international community.

"There were, of course, questions that they were asking about the details that stood behind the agreement, which both the IAEA (International Atomic Energy Agency) and our experts have been answering," Clinton said.

"But the terms of the agreement, the heart of the agreement, is not and will not be altered," she said.

Iran denies western claims that it is bent on producing nuclear weapons, but the crisis escalated in September, when it and the United States revealed the existence of a previously undisclosed nuclear plant inside a mountain near Qom.

From the US point of view, the deal would give Washington and its negotiating partners time to negotiate a more far-reaching agreement with Iran, and defuse the crisis.

Germany is one of the partners, along with China, Russia, France, and Britain.

Westerwelle said he "can only strongly underline what" Clinton said.