Tehran (AFP) - Iran's nuclear chief said Saturday that the country had asked to buy 950 tonnes of uranium concentrate from Kazakhstan over the next three years to help develop its civil reactor programme.

The request has been made to the body that oversees the nuclear deal signed between Iran and world powers in 2015.

Ali Akbar Salehi, head of Iran's Atomic Energy Organisation, told the ISNA news agency that the purchase was supposed to happen "within three years".

"650 tonnes will enter the country in two consignments and 300 tonnes will enter Iran in the third year," he said.

Salehi said the final shipment of concentrate, known as yellow cake, would be turned into uranium hexafluoride gas and sold back to Kazakhstan -- its first international sale of the compound which is used in the uranium enrichment process.

Under the nuclear deal, many of Iran's centrifuges were mothballed but it has the right to enrich uranium to a level of 3.5 percent and sell it abroad.

Nuclear weapons require uranium enriched to 80 percent or more.

Salehi said Iran has already received around 382 tonnes of yellow cake, primarily from Russia, since the nuclear deal came into force in January last year.

Under the deal, Iran is allowed to run around 5,000 "IR-1" centrifuges and has been testing more advanced models that can produce greater quantities of enriched uranium -- all under the strict supervision of the UN atomic agency.