Iran resumed uranium enrichment at its Fordow nuclear facility on Thursday, and it will be enriched to a level of 4.2 percent on Saturday, according to Iranian Atomic Energy Organisation (AEOI).

"Injection of uranium gas to centrifuges started on Thursday at Fordow, and all the process has been supervised by the inspectors of the UN nuclear watchdog," the AEOI said in a statement.

"The process will take a few hours to stabilize and by Saturday, when International Atomic Energy Agency inspectors again visit the site, a uranium enrichment level of 4.2 percent will have been achieved," AEOI's spokesman Behrouz Kamalvandi told state TV.