They have told The Associated Press that Tehran has readied the site for the installation of thousands of new-generation centrifuges. These machines could greatly speed up production of material that can be turned into the core of nuclear warheads.

The diplomats say that electrical circuitry, piping and supporting equipment for the new centrifuges is in place.

They emphasize that Tehran has not started installing the more efficient machines at its Fordow facility and cannot say whether it was planning to.

But the diplomats say Iran has little reason to prepare the ground for the better centrifuges unless it planned to operate them.

The diplomats asked for anonymity because their information is privileged.