A top Iranian official say the country now has 4,000 working nuclear centrifuges.
Deputy Foreign Minister Ali Reza Sheik Attar made the claim to Iranian state media Friday, saying another 3,000 centrifuges will soon be installed at Iran's main nuclear site in Natanz.
The centrifuges could significantly boost Iran's ability to produce enriched uranium.
Iran has repeatedly said the goal of its nuclear program is to generate electricity. But critics - including the United States - fear Iran is trying to develop nuclear warheads. Highly enriched uranium can be used to make nuclear weapons.
International officials last estimated Iran was operating 3,500 uranium-enriching centrifuges at the Natanz facility.
In April, President Ahmadinejad announced plans to install 6,000 new centrifuges.
Iran is under three sets of United Nations sanctions, imposed because of its failure to comply with Security Council orders to halt uranium enrichment. The U.N. has threatened to impose a fourth set if Iran does not freeze its enrichment program.
Iran said Thursday it had agreed to share nuclear technology with Nigeria to help the African nation produce more energy.
Last week, a senior official with Iran's atomic energy agency said the country had started designing its second nuclear power plant.
Iran is still building its first nuclear power plant with Russia's assistance. The 1,000-megawatt plant is located in the southern city of Bushehr.
Some information for this report was provided by AP and Reuters.