Iran faced international condemnation after announcing plans for a massive expansion of its uranium enrichment programme.
Iran had been expected to give a hardline response to an International Atomic Energy Agency vote last Friday condemning it for keeping the construction of the Qom plant secret.
But President Mahmoud Ahmadinejad's reaction was more far-reaching than had been predicted and is expected to heighten tensions further.
Any new enrichment plants would take years to build but the plans were seen as a statement that Iran is willing to risk further sanctions and won't back down amid a deadlock in negotiation attempts.
White House spokesman Robert Gibbs said in a statement: "If true, this would be yet another serious violation of Iran's clear obligations under multiple UN Security Council resolutions and another example of Iran choosing to isolate itself.
"Time is running out for Iran to address the international community's growing concerns about its nuclear programme."
That would risk leaving two rogue states, including North Korea, actively pursuing enriched uranium programmes outside the IAEA's inspection programme.
President Barack Obama would be left with a scenario of being forced either to allow an Israeli military strike on Iran, or face accusations that he had lost control of America's dealings with hostile states.