Iran's nuclear chief said the country is building a new generation of centrifuges for uranium enrichment but that they need further tests before they can be operational, the Associated Press reports.

Under a landmark nuclear deal reached last month between Iran and world powers, Iran promised not to bring new centrifuges into operation for six months. But the deal does not stop it from developing centrifuges.

In comments reported by state TV late Thursday, Dec 26, nuclear chief Ali Akbar Salehi did not elaborate on how long the building and testing would take. He also said Iran has a total of 19,000 centrifuges, though he did not say how many were operational. In August, Iran said it had 18,000 centrifuges.

Iran previously gave the UN nuclear watchdog information on the new generation of machines.