TEHRAN, Iran—Iran’s nuclear chief says Iran now has more than 5,000 centrifuges operating at its uranium enrichment plant.

The announcement Wednesday is Iran’s latest defiance of U.N. demands that Tehran halt its controversial nuclear program.

The Iranian official, Gholam Reza Aghazadeh, says Iran will continue to install centrifuges and enrich uranium in order to produce nuclear fuel for the country’s future nuclear power plants.

Uranium enriched to low level is used to produce nuclear fuel. Further enrichment makes it suitable for use in nuclear weapons.

The new number of working centrifuges is a significant increase from the 4,000

Iran said were up and running in August at the plant in

the central Iranian city of Natanz.