Iran resumed uranium reprocessing activities at its facility in Isfahan last month after it rejected a European package of proposals.
That package had called on Iran to permanently stop its uranium enrichment programme in return for a supply of nuclear fuel and economic incentives.
Iran says it will not give up uranium enrichment, a right granted to it under the Nuclear Non-Proliferation Treaty.
A report by Mohamed ElBaradei, head of the International Atomic Energy Agency, said on Friday that Tehran had recently produced about seven tonnes of the gas it needs to enrich uranium - a possible pathway to a nuclear weapon.
"The issue of Isfahan is a thing of the past. We won't get back it," Foreign Ministry spokesman Hamid Reza Asefi said on Sunday.
The US has accused Iran of using its civilian nuclear programme as a cover to secretly produce nuclear weapons.
Iran has rejected the charges, saying its nuclear programme is geared towards generating electricity, not making a bomb.