Iran has neutralized most of its stockpile of higher-enriched uranium that could be turned quickly into the core of a nuclear weapon, the U.N. nuclear agency said Friday, leaving the country with only about a fifth of what it would need for such a purpose. The International Atomic Energy Agency said in a confidential report that Iran now has less than 40 kilograms (90 pounds) of the material. The report, obtained by The Associated Press, said Tehran also was meeting all other obligations under the agreement, reached four months ago as a prelude to a comprehensive deal now being negotiated. Iran denies any interest in having atomic arms. But it is ending some nuclear activities and limiting others under a first-step plan implemented in January that gives it some sanctions relief in return for the concessions. As part of the deal, Iran agreed to dilute or convert all of its stock of uranium enriched to 20 percent. At that level, uranium is only a technical step away from use as the core of a nuclear warhead. Iran had produced almost enough 20-percent material for such a weapon until it stopped in January and started transforming what it had. The agency was less positive in its assessment of Iran's cooperation with IAEA attempts to probe suspicions -- denied by Tehran -- that it worked secretly on nuclear weapons development. Iran, it said, was engaging on the issue "for the first time ... since 2008," by providing documents on the use of detonators that the agency suspects were part of experiments on setting off a nuclear charge. But the agency said Iran continues to assert that its tests were for civilian use in its documentation.