Western nuclear experts said Wednesday that Tehran lacked the skills, materials and equipment to make good on its immediate nuclear threats, even as a senior Iranian official said that Iran would defy international pressure and rapidly expand its ability to enrich uranium.

The official, Muhammad Saeedi, the deputy head of Iran's atomic energy organization, said that Iran would push to put 54,000 centrifuges on line — a dauntingly vast increase from the 164 which, they said Tuesday, they had successfully used to enrich uranium to levels that could fuel a nuclear reactor.

Still, nuclear analysts said Wednesday that the claims did little or nothing to alter current estimates of when Tehran might be able to make a single nuclear weapon, which some analysts have estimated could be as late as 2015 or even 2020.

Iran's announcement brought criticism from several Western nations and to a lesser degree from Russia and China. The Bush administration took the opportunity to press for "strong steps" against Iran, hoping to use the country's clear statement of defiance to persuade reluctant countries like Russia and China to support tough international penalties. But Russian officials said they had not changed their opposition to such penalties. Nuclear analysts said Iran's boast that it had enriched uranium using 164 centrifuges meant that it had now moved one small but significant step beyond what it had been ready to do nearly three years ago, when it agreed to suspend enrichment while negotiating the fate of its nuclear program.

"They're hyping it," said David Albright, president of the Institute for Science and International Security in Washington, a private group that monitors the Iranian nuclear program. "There's still a lot they have to do."

Anthony H. Cordesman and Khalid R. al-Rodhan of the Center for Strategic and International Studies in Washington called the new Iranian claims "little more than vacuous political posturing" meant to promote Iranian nationalism and a global sense of atomic inevitability.

The nuclear experts said that Iran's claim on Wednesday that it would mass-produce 54,000 centrifuges echoed boasts that it made years ago. Even so, they noted, the Islamic state still lacked the parts and materials to make droves of the highly complex machines, which can spin uranium into fuel rich enough for use in nuclear reactors or weapons.

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