VIENNA, Austria (AP) – International Atomic Energy Agency experts have found unexplained plutonium and highly enriched uranium traces in a nuclear waste facility in Iran and have asked Tehran for details, a report from the U.N. watchdog said Tuesday.

The report, prepared for next week’s meeting of the 35-nation IAEA, also faulted Tehran for not cooperating with the agency’s attempts to investigate suspicious aspects of Iran’s nuclear program that have led to fears it might be interested in developing nuclear arms.

And it said it could not confirm Iranian claims that its nuclear activities were exclusively nonmilitary unless Tehran increased its openness.

“The agency will remain unable to make further progress in its efforts to verify the absence of undeclared nuclear material and activities in Iran,” without additional cooperation from Tehran, said the report, by IAEA chief Mohamed ElBaradei.

Such cooperation is a “prerequisite for the agency to be able to confirm the peaceful nature of Iran’s nuclear program,” it added.

As expected, the four-page report made available to The Associated Press confirmed that Iran continues uranium enrichment experiments in defiance of the U.N. Security Council.

Both highly enriched uranium and plutonium can be used to make the fissile core of nuclear warheads, and Iran is under intense international pressure to freeze activities that can produce such substances.

But Tehran has shrugged off both Security Council demands that it stop developing its enrichment programs and urgings that it cease construction of a heavy water research reactor that produces plutonium waste. It insists it wants enrichment only to generate nuclear power and says it needs the Arak research reactor to produce isotopes for medical research and cancer treatment.

A senior U.N. official who was familiar with the report cautioned against reading too much into the new finds of traces of highly enriched uranium and plutonium, saying Iran had provided explanations for both that were now being examined by the IAEA and – if confirmed – could be plausibly classified as the byproducts of peaceful nuclear activities.

He said that – while the uranium traces were enriched to a higher level than needed to generate power, they were still below weapons-grade.

Still, a series of IAEA reports across nearly four years have revealed a number of suspicious activities, including unexplained plutonium experiments, possession by Iran of diagrams showing how to mold uranium metal into the shape of nuclear warheads and other traces of highly enriched uranium at sites linked to military research. As such the newest findings were likely to be cited by the United States and other nations suspicious of Tehran’s nuclear agenda as adding to circumstantial evidence against it.

As previous reports, Tuesday’s summary listed specific cases of lack of cooperation by Tehran with agency inspectors.

These included refusal to allow the agency to boost monitoring of its enrichment facilities at Natanz; lack of response to request for more information on its enrichment program; denial of access to suspicious equipment and to military personnel possibly involved in nuclear activities; denial of a request for a copy of the uranium metal diagrams; and refusal to provide information on apparent experiments linking nuclear and ballistic missile research.