Ambassadors at the United Nations nuclear agency are expected to defer an Iranian request for help to complete a plutonium reactor near Tehran.
Western diplomats say the International Atomic Energy Agency will postpone a decision on technical aid when officials meet in Vienna on Thursday. Diplomats likely will approve assistance for seven other requests from Iran, including aid for safety and regulatory projects.
Iran says the reactor in Arak is to open in 2009 and will produce isotopes for medical use.
The U.S. ambassador to the nuclear agency, Gregory Schulte, says the Arak reactor could produce nuclear material for a weapon, and says it should be opposed.
Ambassadors for several developing nations say they support the aid request.
Tehran denies claims by Western nations that it is seeking nuclear weapons.
In August, Iran defied a United Nations deadline to stop enriching uranium at a separate site in the country. The U.N. Security Council is considering sanctions against Iran because of the move.
Some information for this report was provided by AFP, AP and Reuters.