The state-run IRNA news agency on Monday quoted Ali Rabiei as saying that President Hassan Rouhani has given the order for the move at the Fordo facility.
Enrichment at 20 per cent is a short, technical step away from weapons-grade levels of 90 per cent.
Iran’s decision to begin enriching to 20 per cent a decade ago nearly brought an Israeli strike targeting its nuclear facilities, tensions that only abated with the 2015 atomic deal. A resumption of 20 per cent enrichment could see that brinksmanship return.
The move comes after President Donald Trump withdrew the US unilaterally from Iran‘s nuclear deal with world powers in 2018. In the time since, there have been a series of escalating incidents between the two countries.