Two intelligence officials briefed on the damage said it had been caused by a large explosion that completely destroyed the independent — and heavily protected — internal power system that supplies the underground centrifuges that enrich uranium. The officials, who spoke on the condition of anonymity to describe a classified Israeli operation, said that the explosion had dealt a severe blow to Iran’s ability to enrich uranium and that it could take at least nine months to restore Natanz’s production... The blackout came less than year after a mysterious fire ravaged another part of the Natanz facility, about 155 miles south of Tehran, the capital. Iranian officials initially played down the effect of the fire, which destroyed an above-the-ground facility for the assembly of centrifuges, but later admitted that it had caused extensive damage... Some Iranian experts dismissed initial speculation that a cyberattack could have caused the power loss. The Natanz complex has its own power grid, multiple backup systems and layers of security protection intended to stop such an attack from abruptly shutting down its system.