Iranian President Mahmoud Ahmadinejad says his country has expanded a key nuclear process that the United Nations Security Council demanded it stop.
Mr. Ahmadinejad told a ceremony on Monday at Iran's nuclear facility at Natanz that Iran is enriching uranium on an "industrial scale."
Iran's top nuclear negotiator, Ali Larijani, said Iran had begun to feed uranium gas into three thousand centrifuges for enrichment -- a major expansion of the process.
The UN Security Council has passed two resolutions imposing sanctions on Iran since December for its refusal to suspend uranium enrichment, a process which can be used to make nuclear weapons.
US State Department spokesman Sean McCormack said the Iranian president's speech shows Iran's continued defiance of the international community. The spokesman said the speech showed that UN action against Iran is legitimate and justified.
McCormack said he hopes "reasonable" Iranian leaders will see that continued defiance does not benefit Iran.
The head of Iran's nuclear energy agency Gholam Reza Aghazadeh told the ceremony that Iran is starting to mass-produce the centrifuges needed to enrich uranium.
Iranian nuclear negotiator Larijani also said that Iran would have to reconsider its membership in the nuclear Non-Proliferation Treaty -- if it is subjected to further pressure over its nuclear program.
The United States and its allies accuse Iran of trying to develop nuclear weapons. Iran says its nuclear program is for the peaceful production of energy.