A new U.N. report on Iran's nuclear program says that the latest effort to probe allegations of secret work on atomic arms by Tehran has failed to make headway.

Iran agreed in February to cooperate in restarting the investigation by the U.N.'s International Atomic Energy Agency, after a decade of deadlock.

Since then, the U.N. agency has sought information on alleged experiments with detonators that can be used to set off nuclear explosions; separate work on high-explosive charges used in nuclear blasts, and alleged studies on calculating nuclear explosive yields.

The confidential IAEA report, issued Friday, made clear that there has been little progress.

Iran insists that it never worked on such arms.

The report comes two days after diplomats told The Associated Press that the probe was stalled.