Iran has submitted a letter to the International Atomic Energy Agency outlining an agreement to send its enriched uranium abroad.
The letter, delivered Monday (at 0830 UTC), outlines the plan in which Iran will send 1,200 kilograms of low-enriched uranium to Turkey for higher-enriched fuel for a medical research reactor in Tehran.
The agreement among Iran, Brazil and Turkey was reached last week.
World powers have expressed doubt about the offer, saying the amount of the fuel Iran has offered to swap is only about half the country's stockpile.
The United States and its Western allies accuse Iran of trying to build a nuclear bomb. Iran says its atomic program is for peaceful purposes.
Last week, the U.S. and other world powers approved a draft U.N. resolution that would impose a fourth round of sanctions on Iran because of its refusal to stop enriching uranium.
On Sunday, Iran parliament speaker Ali Larijani said the deal will be nullified if the United States takes steps through the U.N. Security Council or U.S. Congress to impose sanctions.
He said Iran may also review its cooperation with the International Atomic Energy Agency.
Some information for this report was provided by AFP and Reuters.