UNITED NATIONS - United Nations nuclear officials were in apparent disagreement with Washington over U.S. claims that it had the proper authority to transfer highly radioactive material from Iraq last month.

The nearly 2 tons of low-enriched uranium and approximately 1,000 highly radioactive items could be used in so-called "dirty bombs." The material had been placed under seal by the International Atomic Energy Agency at the Tuwaitha nuclear complex, 12 miles south of Baghdad, U.N. officials said Wednesday.

The United States disclosed Tuesday that the material was secured from Iraq's former nuclear research facility and airlifted out of the country to an undisclosed Energy Department laboratory for further analysis last month.

"The American authorities just informed us of their intention to remove the materials, but they never sought authorization from us," said Gustavo Zlauvinen, head of the IAEA's New York office.

Under U.N. resolutions adopted after the 1991 Gulf War, the IAEA was authorized to oversee the destruction of Iraq's nuclear program and monitor its activities to ensure that the program was not revived.

Paul Longsworth, deputy administrator for defense nuclear nonproliferation in the U.S. National Nuclear Security Administration, said Wednesday the United States didn't need IAEA approval for the transfer.

"We believe we have the legal authority to do it," he said. "We are in custody of the material only, and we have the permission of the Iraqi government to take this out of the country."

U.S. Energy Secretary Spencer Abraham, in disclosing the secret airlift Tuesday, called it "a major achievement" in efforts to "keep potentially dangerous nuclear material out of the hands of terrorists."

The airlift ended on June 23, five days before the United States transferred sovereignty to Iraq's new interim government.

In 1992, after the first Gulf War, all highly enriched uranium - which could be used to make nuclear weapons - was shipped from Iraq to Russia, the IAEA's Zlauvinen said.

After 1992, roughly 2 tons of natural uranium, or yellow cake, some low enriched uranium and some depleted uranium was left at Tuwaitha under IAEA seal and control, he said.