TEHRAN  Iran announced on Tuesday a significant expansion of its plans to enrich uranium despite the United Nations Security Council’s demand that it halt the program. President Mahmoud Ahmadinejad said during a visit to Iran’s main enrichment complex at Natanz that the country had started installing 6,000 centrifuges at the site, in addition to the existing 3,000 centrifuges.

Western experts cautioned that Iran’s technical claims often exceeded its grasp, and in the past they have greeted such pronouncements by Iran with skepticism. While they have confirmed that Iran has 3,000 operating centrifuges, there was no confirmation of the latest claims.

If Iran carries out its plans, it will triple the size of its industrial base and produce a major expansion in its uranium enrichment program. Enrichment can make fuel for civilian nuclear reactors or, if taken to higher levels, nuclear warheads.

The United States and other Western countries have accused Iran of having a clandestine nuclear arms program, but Iran says its program is peaceful and for civilian purposes only.