U.S. officials reportedly told Israel that the United States has improved weapons capable of destroying Iran's underground nuclear site in Fordow.
The White House said reports of an explosion at an Iranian nuclear facility were not credible.
Iran is set to sharply expand its uranium enrichment in an underground site after installing all the centrifuges it was built for, a U.N. nuclear report showed on Friday, a move that could increase Western alarm about Tehran's nuclear course.
Iran is believed to be further increasing its uranium enrichment capacity at its Fordow plant buried deep underground, Western diplomats say, in another sign of Tehran defying international demands to curb its disputed nuclear program.
Iran may have installed as many as "hundreds of new" uranium enrichment machines in its underground nuclear facility at Fordow.