Iran says it has converted several tons of raw uranium - also known as "yellowcake" - into a gas that can be used in making enriched uranium.
Iran's chief delegate to the International Atomic Energy Agency, Hossein Mousavian, said Wednesday the amount was not large and was done only for experimental purposes.
Last month, the International Atomic Energy Agency passed a resolution demanding that Iran freeze all enrichment activities. This current move could be seen by some countries as defying the U.N. resolution.
In Vienna, a U.N. atomic agency spokeswoman, Melissa Fleming, said the uranium conversion was being conducted under the close supervision of the IAEA.
At the U.S. State Department, Spokesman Adam Ereli said Iran's latest move "clearly indicates that Iran is continuing its efforts in a nuclear weapons program."