Istanbul, Turkey ? Iran plans to convert 37 tons of uranium into a substance that could be used to manufacture nuclear weapons, the U.N. nuclear watchdog agency said in a report Wednesday.

Although the Iranian plans do not violate nonproliferation regulations because the material also has peaceful uses, they immediately stoked concern in Washington about the aims of Tehran’s ambitious nuclear program.

“Iran’s announcements are further strong evidence of the compelling need to take Iran’s nuclear program to the Security Council,” said U.S. undersecretary of State John Bolton, who called Iran’s nuclear efforts a “threat to international peace and security.”

Iran’s intentions were disclosed in a confidential report prepared by the International Atomic Energy Agency, which was obtained by the Los Angeles Times.

Iran insists that its nuclear program is intended solely to generate electricity, but the United States has repeatedly accused Tehran of concealing a weapons program behind a civilian facade.

In its sixth report on the Iranian program, the atomic agency gave it mixed marks. It praised Iran for cooperating on many fronts, but said key aspects of its nuclear activities were still unclear because of missing information.

The two primary areas of concern are the sources of uranium contamination found at four separate locations during the past year in Iran and the extent of the country’s efforts to develop advanced centrifuges for turning uranium gas into enriched uranium, which can be used in weapons or to fuel civilian reactors.

The IAEA report said that Iranian officials told the agency earlier this summer that they were planning to convert 37 tons of “yellowcake,” milled uranium, into uranium hexafluoride gas. Experts said the gas could be used to produce enough highly enriched uranium for several nuclear bombs or to fuel civilian reactors.