The Mehr news agency quoted Abdulreza Rahmani-Fazli, deputy secretary of the Supreme National Security Council, as saying more centrifuges have been installed at the plant.
Centrifuges can make fuel for nuclear power plants or produce material for atomic weapons.
Iran insists its nuclear plans are peaceful.
Western powers are concerned that Iran is trying to develop a nuclear bomb, and the International Atomic Energy Agency has said it does not have sufficient evidence to conclude that Tehran's nuclear program is not linked to weapons efforts.
U.S. President George W. Bush said on May 17 that the United States and Britain would seek new UN sanctions against Iran if it continued to resist calls for it to halt sensitive areas of its nuclear program.
Bush was speaking at the White House alongside outgoing British Prime Minister Tony Blair.
The U.S. president said Washington and London would "continue to make it clear that Iran with a nuclear weapon is not in the interest of peace in the world."
Bush has said in the past that he regards the prospect of Iran possessing nuclear weapons as "unacceptable."
The UN Security Council has approved two sets of sanctions in its effort to dissuade Tehran from pursuing some nuclear steps, including uranium enrichment.
A control panel at the Bushehr nuclear power plant (Fars)
CASCADES AND CENTRIFUGES: Experts and pundits alike continue to debate the goals and status of Iran's nuclear program. It remains unclear whether the program is, as Tehran insists, a purely peaceful enegy project or, as the United States claims, part of an effort to acquire nuclear weapons.
On June 7, 2006, RFE/RL correspondent Charles Recknagel spoke with nuclear expert Shannon Kile of the Stockholm International Peace Research Institute in Sweden to help sort through some of the technical issues involved. "[Natanz] will be quite a large plant," Kile said. "There will be about 50,000 centrifuges and how much enriched uranium that can produce [is] hard to say because the efficiency of the centrifuges is not really known yet. But it would clearly be enough to be able to produce enough [highly-enriched uranium] for a nuclear weapon in fairly short order, if that's the route that they chose to go...." (more)