Iran has begun putting down piping and electric cables for its underground uranium enrichment plant, with hundreds of workers being employed to move ahead quickly with the program that can be misused to make nuclear arms, diplomats said Friday.

The move marks an escalation of the confrontation between Tehran and the world's major powers over the Islamic republic's nuclear program. Iran says it wants to develop enrichment to generate power, but the United States and dozens of other countries fear it will use the material gained for the fissile core of nuclear warheads.

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One of three diplomats accredited to the International Atomic Energy Agency, which monitors Iran's nuclear program, said that hundreds of technicians and laborers "were working feverishly" at the Natanz underground facility, laying down pipes and wiring needed for the centrifuges that spin uranium into enriched levels.

The diplomat spoke on condition of anonymity because the information was confidential.

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