Iran has begun uranium enrichment at a heavily fortified site near the holy city of Qom, the UN has confirmed.
The International Atomic Energy Agency (IAEA) – the UN’s nuclear watchdog – said the process had begun at the underground Fordo plant.
Iran says it plans to carry out medium-level uranium enrichment – which, say analysts, is an important step towards making it weapons-grade.
Tehran insists its nuclear programme is for peaceful energy purposes.
The existence of Fordo in the north of the country only came to light after it was identified by Western intelligence agencies in September 2009.