The deputy secretary of the Supreme National Council, Javad Vaeidi, told reporters on Tuesday that enrichment of uranium resumed last week at Iran's main enrichment plant in Natanz.
Asked if Iran had resumed large-scale enrichment, as required for producing fuel for nuclear reactors, Vaeidi replied: "No".
"We need time to have 60,000 centrifuges," he said, referring to the devices used in the enrichment process.
Diplomats in Vienna, Austria, the site of the UN nuclear agency, had said on Monday that Iran had started small-scale enrichment of uranium, a process that can produce fuel for an atomic bomb.
UN Security Council
The world has long sought to stop Iran from enriching uranium, fearing that the process would bring it to the threshold of possessing nuclear bombs.
On 4 February the International Atomic Energy Agency reported Iran to the UN Security Council and simultaneously called on its government to suspend all enrichment-related activities.
Instead, the Iranian government decided to suspend certain aspects of its co-operation with the IAEA and steam ahead with enrichment.
Valeidi told the press conference: "According to the presidential order (last week), and to the law passed by the parliament (last year), the order of resumption of uranium enrichment was issued."