Iran's defiance will likely heighten tensions with the West, which has signaled it is running out of patience with Iran's continuing enrichment and its balking at a U.N. deal aimed at ensuring Tehran cannot build a nuclear weapon in the near-term future. The U.S. and its allies have hinted at new U.N. sanctions if Iran does not respond.

The White House said the move "would be yet another serious violation of Iran's clear obligations under multiple U.N. Security Council resolutions and another example of Iran choosing to isolate itself."

"Should the West continue to pressure us, the legislature can reconsider the level of Iran's cooperation with the IAEA," Larijani told parliament in a speech carried live on state radio.

On Sunday, a Cabinet meeting headed by President Mahmoud Ahmadinejad ordered the Atomic Energy Organization of Iran to begin building five uranium enrichment plants at sites that have already been studied and propose five other locations for future construction within two months, the state news agency IRNA reported. All would be at the same scale as Natanz.

The new sites are to be built inside mountains to protect them from possible attacks, said Vice President Ali Akbar Salehi, who is also Iran's nuclear chief. They will also use a new generation of more efficient and more productive centrifuges that Iran has been working to construct, he and Ahmadinejad said.