Iran vowed Sunday to build 10 additional uranium enrichment plants and to counter opponents' potential military strikes by hiding the plants deep in mountains throughout the Islamic republic.
The decree from Iran's Cabinet was perhaps the most unequivocal rejection of Western-led efforts to negotiate a peaceful end to the nuclear standoff with Iran, and it triggered immediate rebukes from the U.S. and other nations.
Iran said it acted in response to censure by the U.N. International Atomic Energy Agency (IAEA) two days earlier over a newly discovered uranium enrichment site that Iran had not acknowledged until recently.
"The decision taken today is a firm reply to the indecent move by the five plus one in the latest IAEA meeting," said Ali Akbar Salehi, a vice president and Iran's top nuclear official.
Five plus one refers to permanent members of the U.N. Security Council plus Germany, which together spearheaded Friday's action by the IAEA.
"Ten new enrichment sites will be built. We are as much committed to our rights as we are to our international obligations," Mr. Salehi said Sunday, according to Iranian state media.
"From now on, our enrichment sites will not be built in the open air but in the hearts of mountains. ... They will not be concentrated in one area ... taking into consideration all safety measures from any attacks."
Israel has threatened and reportedly sought U.S. backing for military strikes against Iranian nuclear facilities. The U.S. likewise has not ruled out military action.
"Our patience and that of the international community is limited, and time is running out," White House spokesman Robert Gibbs said. The IAEA and the United Nations "have to enforce the rules of the road."
British Foreign Secretary David Miliband called Iran's latest move provocative.
"This epitomizes the fundamental problem that we face with Iran," Mr. Miliband said. "We have stated over and again that we recognize Iran's right to a civilian nuclear program, but they must restore international confidence in their intentions. Instead of engaging with us, Iran chooses to provoke and dissemble."
Iran says its expanding nuclear ambitions are peaceful and intended to produce electricity.
"We need some 500,000 centrifuges to produce fuel for the power plants under construction to generate 20,000 megawatts of electricity for domestic use," Iranian President Mahmoud Ahmadinejad said Sunday, according to state media.
Enriched uranium can fuel nuclear power plants. When enriched to a purer level, it can provide the explosive core of atomic bombs, such as the one dropped on Hiroshima at the close of World War II.
Attempts by Iran to hide much of its nuclear activities for more than two decades have enhanced suspicions that its nuclear goals are military.
The U.N. Security Council already has imposed several sets of mild sanctions on Iran because of its nuclear efforts. In recent days, the U.S. has sought support for tougher measures against Iran - measures that have been blocked by Russia and China in the past.
Friday's IAEA censure was unusual because it won support from both China and Russia, which have close commercial links with Iran.
Iran has one uranium enrichment facility operating at Nantaz, considered capable of making enough fuel for about one nuclear bomb each year.
The recent disclosure of the second site, inside a mountain near the holy city of Qom, has reinforced fears that Iran continues to hide much of its nuclear program from outside inspectors.
Prior to Friday's censure by the IAEA, Iran had rejected an IAEA-brokered deal that would have exported Iran's existing supply of low-enriched uranium to Russia or another country, where it would be converted into fuel rods for a medical reactor and returned to Iran.