With thousands of advanced centrifuges on standby, Tehran says it is now spinning more, which could increase its stockpile of near-bomb-grade atomic fuel.

Iran said Friday it would begin operating new machines to enrich more uranium, which could bring it closer to having a weapon. The move came in response to a censure by the International Atomic Energy Agency for failing to cooperate fully with atomic inspectors.

The announcement did not say how many of the machines began spinning, nor how much uranium they will produce. But Western experts said Iran’s act could initiate a significant escalation in the moves and countermoves between Tehran and the U.N. nuclear inspectors based in Vienna, who have struggled for decades to keep the nation from getting the means to make an atom bomb.

Iran will activate “a substantial number of advanced centrifuges of various models,” which are able to produce highly enriched nuclear fuel, read a joint statement from Iran’s Foreign Ministry and its Atomic Energy Organization. It condemned the censure as “politicized and destructive,” saying it undermined “the positive momentum” achieved between Iran and the I.A.E.A.

Behrouz Kamalvandi, a spokesman for Iran’s Atomic Energy Organization, said Friday in an interview with media in Iran that the country began accelerating its enrichment right after the order was announced. “We immediately started,” he was quoted as saying. “We will significantly increase enrichment.”

Having a supply of highly enriched uranium fuel is just one step of many it would take to build a deliverable atom bomb. Other crucial steps include turning the material into a metallic sphere and making arrays of explosive detonators, and may take many more months to complete.

Late Thursday in Vienna, the Board of Governors of the International Atomic Energy Agency voted 19 to 3, with 12 abstentions, for Iran’s censure. The move could lead to penalties against Tehran, including new economic sanctions. The agency sees the censure step as exercising its mandate to try to keep the world’s peaceful nuclear programs from crossing lines that would let them make warheads.

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