IAEA director: Everybody looked to the future, not the past
Iran and three world powers have been handed a draft agreement aimed at reducing international concerns over Tehran's nuclear programme.
The International Atomic Energy Agency, which proposed the plan after talks in Vienna, wants an answer by Friday.
Details are yet to be confirmed, but the plan is believed to involve Iran exporting uranium to be enriched in France and Russia.
Iran's chief negotiator has not commented on the uranium export plan.
The negotiations have involved the UN, Iran, France, Russia and the US.
IAEA director Mohamed ElBaradei told reporters in Vienna that he was feeling "optimistic" after the talks, which he said had been "very constructive".
Jon Leyne, BBC Tehran correspondent
Under the draft plan Iran would send around 1200kg, the majority of its stocks of enriched uranium, to Russia and then to France before it is returned to run a research reactor in Tehran.
The big advantage for the West is that the arrangement would neutralise most of Iran's stockpile of enriched uranium. At the very least this would delay Iran's ability to make a nuclear bomb.
But no Iranian official has yet publicly acknowledged that Iran's enriched uranium would be shipped out of the country.
There must be doubts whether President Mahmoud Ahmadinejad's government is really willing to allow its hard-won enriched uranium out of its grasp, particularly as Mr Ahmadinejad has turned the nuclear programme into such a matter of national pride.
But for the West, that key component of the agreement would surely be the deal-breaker.
"Everybody at the meeting was trying to help, trying to look to the future and not to the past, trying to heal the wounds that existed for many years," he said.
"I have circulated a draft agreement that in my judgment reflects a balanced approach to how to move forward."
Russian nuclear industry insiders told the BBC the process proposed would involve Iran sending its uranium to the IAEA, which would forward it to Russia for enriching.
The enriched uranium would then be returned to the IAEA and sent to France, which has the technology to add the "cell elements" needed for Iran's reactor, they said.
This process would enable Iran to obtain enough enriched uranium for its research reactor, but not enough to produce a weapon.
Exporting uranium has been seen as a way for Iran to get the fuel it needs, while giving guarantees to the West that it will not be used for nuclear weapons.
Iranian chief negotiator Ali Asghar Soltaniyeh talked positively about a deal, but did not mention uranium export.
Mr ElBaradei said there had been many technical, legal and policy issues to address in the Vienna talks, as well as "issues of confidence and trust".
"That is why it has taken us some time and that is why we need to send the agreement to capitals for final approval," he added.
"I very much hope that people see the big picture - that this agreement could pave the way for a complete normalisation of relations between Iran and the international community."
US Secretary of State Hillary Clinton urged Iran to act quickly, and said her country would continue "to discuss the full range of issues that have divided Iran and the United States for too long".
She added: "The door is open to a better future for Iran, but the process of engagement cannot be open-ended. We are not prepared to talk just for the sake of talking."
France said the plan was acceptable and would benefit Paris and its partners.
Foreign ministry political director Jacques Audibert told France 24 television that the plan was "to remove this (uranium) from Iran, use it to make the fuel they need and thereby improve relations and lower the tensions over Iran's civilian nuclear programme."
Iran insists its nuclear programme is solely for peaceful purposes and that it has the right to enrich uranium.
Western states believe it is attempting to develop a nuclear weapons programme.
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