The US government has warned Iran that its continued enrichment of uranium meant that any new international offer on Tehran’s nuclear program would be more burdensome than the one the Iranian regime had already rejected. White House spokesman Robert Gibbs said increased expectations required for any deal reflected the fact that Iran's enriched uranium stocks were now larger than they were when previous talks broke down last year. "Based on the unilateral actions that they took, they have increased their enrichment. In order to live up to the responsibilities that they have made and to lift any sanctions, they would have great responsibilities," Gibbs said, adding: "The responsibilities get greater each and every day even as the sanctions impact their economy more and more."

Gibbs spoke after the ‘New York Times’ published a report that the Obama administration and its European allies were preparing a new, more onerous offer for Iran than the one rejected by Tehran last year. Under the proposed deal, Iran to send more than around 2,000 kilograms of low-enriched uranium out of the country, an increase of more than two-thirds from the amount required under a deal reached last year but later rejected by Iran’s Supreme Leader Ayatollah Ali Khamenei. Iran would also have to stop producing nuclear fuel that is enriched to 20 percent, and agree to negotiate on the nuclear program's future. The amount of uranium to be sent out of Iran would be over two-thirds greater than the amount requested in Vienna last year. 

"This will be a first sounding about whether the Iranians still think they can tough it out or are ready to negotiate," an unnamed senior American official was quoted by the newspaper as saying. "We have to convince them that life will get worse, not better, if they don't begin to move."

Western diplomats in Vienna, where the International Atomic Energy Agency is located, told the ‘Reuters’ news agency that they believe the reported new offer will fail. Another senior US official said the United States and its European partners were "very close to having an agreement" to present to Iran. However, Tehran has yet to respond to a request by EU foreign policy chief Catherine Ashton, who represents world powers in the nuclear dialogue with Iran, to meet in Vienna in mid-November.

Meanwhile, the US Treasury Department has blacklisted dozens of Iranian "front companies" in Europe that are said to be supporting nuclear weapons efforts.