The U.N. nuclear agency is confirming that Iran has shrouded a site where suspected work on developing nuclear arms took place and says its work on trying establish what went on there is now "significantly hampered."

In a report, the International Atomic Energy Agency also says that Iran has installed about 1,000 of new machines used to make material that can be used to make nuclear warheads at an underground site fortified from air attack.

Enrichment can make both reactor fuel and the core of nuclear warheads, and the underground Fordo plant already has hundreds of centrifuges enriching to a level that is higher than needed for fuel and closer to what is needed to make weapons

Iran denies any interest in nuclear arms.