Iran, the United States, France and Russia have until Friday to approve a draft deal on transfer of most of Iran's nuclear fuel, the U.N. nuclear agency said.

Negotiators for the four countries had been meeting in Vienna the past several days trying to resolve Iran's nuclear fuel issue before the tentative agreement was struck Wednesday, the United Nations said. Western negotiators want Iran to ship its nuclear material to third-party countries so it can be enriched and converted for medical purposes once the material returns to Iran.

While not revealing the contents of the deal, International Atomic Energy Agency Director General Mohamed ElBaradei, in a news release, called it a "balanced approach on how to move forward."

ElBaradei expressed optimism the countries would endorse the draft agreement, which he called a "very important confidence-building measure that can defuse the crisis that has been going on for a number of years and open space for negotiations."

The fuel is used at a Tehran research reactor, which produces medical radioisotopes for therapeutic and diagnostic procedures.

If the draft agreement is approved by the four countries, it would be forwarded to the IAEA Board of Governors for formal ratification.

"I must say that everybody who participated 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, many years," ElBaradei noted.

Iran maintains its nuclear program is for peaceful purposes, but some Western countries contend it is to develop nuclear weapons capability.