Uranium enriched to low level is used to produce nuclear fuel. Further enrichment makes it suitable for use in nuclear weapons.
The United States and some of its allies accuse Iran of seeking to build nuclear weapons. Tehran denies the claim and insists it has the right under the Nuclear Nonproliferation Treaty to enrich uranium and produce reactor fuel.
"At this point, more than 5,000 centrifuges are operating in Natanz," said Aghazadeh, who is head of the Atomic Energy Organization of Iran. He spoke to reporters during an exhibition of Iranian nuclear achievements at Tehran University.
The United Nations Security Council has already imposed three rounds of sanctions on Iran for its refusal to freeze the uranium enrichment program.
In the process, uranium gas is spun in a series of centrifuges known as "cascades" to purify it. Lower levels of enrichment produce reactor fuel but higher grades can build a weapon.
At the exhibition, Iran for the first time put on public display one of its P-1 centrifuges and officials at the exhibition explained various parts of machine to visitors.
The P-1 centrifuge is the workhorse of Iran's enrichment program. It's run in cascades of 164 machines.
In February, Iranian officials confirmed that they have started using the IR-2 centrifuge, which can churn out enriched uranium at more than double the rate of P-1.
Iran has said it plans to move toward large-scale uranium enrichment that will ultimately involve 54,000 centrifuges.