Iran has reported an accident at its main nuclear facility at Natanz.
Tehran's Atomic Agency says it affected the site's electrical distribution grid.
Power was out across the facility's above-ground workshops and underground enrichment halls.
On Saturday, President Hassan Rouhani said Tehran had launched new advanced enrichment centrifuges at the site.
This is after several centrifuges were damaged in a fire last year - an incident Tehran called an 'act of sabotage'.
And Iran is high on the agenda as the U-S Secretary of Defence Lloyd Austin visits Israel.
Tensions in the region have been escalating in recent weeks.