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This story was filed by CBS News correspondent Elizabeth Palmer in Vienna. CBSNews.com's Tucker Reals in London contributed to the report.
Diplomats from Iran, the U.S., Russia and France agreed Wednesday to a draft proposal that would see Iran ship about 75 percent of its enriched uranium to Russia by the end of this year.
Each nation's government will still need to ratify the agreement individually by Friday, and it's unclear whether Iran's hard-line rulers intend to do so.
Iran's envoy was upbeat following the morning talks. Lead negotiator Ali Asghar Soltanieh told reporters upon emerging from the closed door meetings that a side deal attached to the proposal includes an historic first: a proposed direct transfer of U.S. nuclear technology to Iran, including "control, instrument and safety equipment" for the research reactor at Tehran University.
Above: Iran's Ambassador to the International Atomic Energy Agency, IAEA, Ali Asghar Soltanieh, left, speaks to media after talks between Iran and the United States, Russia and France over Iran's nuclear program, Oct. 21, 2009, at Vienna's International Center.
That deal, which the American side has not yet confirmed to CBS News, would be monitored and facilitated by the UN's International Atomic Energy Agency.
"We have been informed about the readiness of the United States, in a technical project with the IAEA, to cooperate in this respect," said Soltanieh. "This will be also further elaborated at a later stage," he added.
Filed at 6:40 a.m. Eastern:
Diplomats from Iran, the U.S., France and Russia resumed meetings Wednesday in Vienna, Austria seeking agreement on a deal that would see Iran move the majority of its enriched uranium stockpile out of the country before the end of this year.
Iran agreed in principle a month ago that the uranium should go to Russia and France for re-processing into fuel rods for medical use in their old, U.S.-built research reactor at the University of Tehran.
The Obama administration and its allies in Europe are pushing for the deal because it would move the uranium out of the Islamic Republic's reach for any potential military purposes.
Iran could make another equivalent stockpile of enriched uranium — theoretically enough for a bomb — but it would take about two years. The country's leaders have always insisted their nuclear intentions are peaceful, but the U.S. and many European nations fear they are hiding a clandestine weapons program.
Senior American officials said before heading back into the talks that negotiations would end Wednesday, but that the outcome was still far from clear.
Asked whether a deal was within reach they said, "We just can't tell."
Describing the talks as "classic negotiation," the U.S. officials said that, even after a day and a half of hard bargaining, none of the outstanding issues had been completely resolved.
It's believed the two main sticking points are the quantity of uranium Iran will ship abroad for re-enrichment, and how soon they will do it.
Foreign Minister Bernard Kouchner laid out France's terms for the deal Tuesday in Paris. "It must be before the end of the year," he said, and Iran must send, "at least 1,200 kilograms" (2,600 pounds, or about 75% of their stockpile) of its enriched uranium to Russia to be re-processed.
Wednesday night, the head of the United Nations nuclear watchdog agency, which is also taking part in the talks, said they were making progress on the technical issues — including the "how much and when" questions, and costs.
"The door is wide open for Iran. If they want this deal, all they have to do is say yes and there will be one," said International Atomic Energy Agency chief Mohammed ElBaradei.
American officials have continued talks with Iran in Vienna even as the Islamic Republic moved Tuesday to sentence American-Iranian academic Kian Tajbaksh to 12 years in jail for policital reasons.
The White House has choosen to deal with the various Iran issues one at a time. While Tajbaksh's sentence has angered the Obama administration, there is hope that a nuclear deal with Iran could set the stage for a more constructive relationship overall on all matters, including human rights.