"It was decided to create a more modern, larger and more improved station in the heart of the mountains around Natanz, and the implementation of this project has started," Ali Akbar Salehi, the head of Iran's atomic agency, said on state television.

"We started the preliminary work by supplying the equipment and setting up a series of production chambers for advanced centrifuges," he added, without giving further details.

Advanced centrifuges are used in the process of uranium enrichment.

Iran said last month that an explosion at its plant in Natanz had been caused by "sabotage".

After the July explosion, Iran sent warnings to Washington and Israel, two countries which accuse Tehran of developing a secret military nuclear programme, claims Iran has always denied.

On Sunday, Iranian atomic energy spokesman Behrouz Kamalvandi said that after investigations into the Natanz explosion they had identified the "elements" responsible. No further details were given.

The 2015 nuclear agreement has been faltering since US President Donald Trump unilaterally withdrew in 2018 from an international accord that gave Iran relief from sanctions in exchange for curbs on its nuclear programme.

In retaliation to the US withdrawal, the Islamic republic started producing uranium at a higher grade than allowed under the deal.

Last week, the UN's nuclear watchdog said that Iran's stockpile of enriched uranium stands at more than ten times the limit set down in the 2015 nuclear deal.