Vienna, Austria ? Hundreds of workers in Iran have set up piping, control panels and electric cables for Tehran’s underground uranium enrichment plant, diplomats said Friday – the final step before installing equipment that countries fear could be used to make nuclear arms.

The move marks an escalation of the confrontation between Tehran and the world’s major powers over the Islamic republic’s nuclear program and will likely spur U.S. efforts to sharpen existing U.N. sanctions slapped on Iran for its defiance of a Security Council demand that it freeze enrichment efforts.

A top Iranian nuclear official said U.N. inspectors have set up cameras in Natanz to monitor the activity. The official, speaking on condition of anonymity because he was not authorized to give statements to the media, said the cameras were put in place over the past few days, ending Thursday.

Iran says it wants to develop enrichment to generate power, but the United States and other countries fear Tehran will use the material for the fissile core of nuclear warheads.

“This work is not necessary for a peaceful nuclear energy program but is needed to give Iran’s leaders the know-how to make highly enriched uranium for nuclear weapons,” said Matt Boland, spokesman for the U.S. delegation to the International Atomic Energy Agency.

Another diplomat accredited to the Vienna-based IAEA, which monitors Iran’s nuclear program, said hundreds of technicians and laborers had been “working feverishly” at the Natanz underground facility over the past few weeks. By Thursday, pipes, wiring, control panels and air conditioning had been installed – setting the stage for hooking up the centrifuges that spin uranium into enriched levels.

The diplomat was one of four who spoke to The Associated Press on condition of anonymity because the information is confidential.

The diplomats emphasized that the work at the plant was preliminary. But one said centrifuges already were being lowered by freight elevators into the facility, along with other equipment needed to assemble “cascades” – centrifuges in series that spin and re-spin uranium gas to the required level of enrichment. They said to their knowledge, no centrifuges had been set up by Thursday.

“Everything is done except putting the machines in and hooking them up,” one of the diplomats said.