Diplomats in Vienna say they are on the verge of a deal that could reduce fears about Iran's nuclear weapons by shipping uranium to Russia.
The agreement between the U.S., France, Russia and Iran calls for Iran to send most of its low grade enriched uranium to Russia in exchange for higher grade fuel alloys. This makes it tougher for Tehran to build nuclear bombs.
"It is a very important confidence building measure that could defuse a conflict that has been going on for years," said Mohamed El Baradei of the Atomic Energy Agency.
Although Iran's negotiator was at the bargaining table, the ruling Mullahs still have not signed off on the deal. All of the parties hope the bill will be signed by Friday.
The Obama administration has insisted on talking first with Iran before imposing strong sanctions or taking military action.
Secretary of State Hillary Clinton suggested the agreement could be a test.
"If Iran is serious about taking practical steps to address the international community's deep concerns about its nuclear program, we will continue to engage both multilaterally and bilaterally," she said.
Even if the agreement is signed, critics of dialogue with Iran will warn that the regime is only stalling for time.
For years Iran has secretly stored enriched uranium and lied about its nuclear weapons program.
Meanwhile, skeptics say Tehran will keep building the weapons that will give it maximum leverage in its struggle to be a global power.