Alarmed by reports of widespread looting at Iraq's main nuclear site, the head of the U.N. nuclear watchdog has asked the United States to let it send a mission to the facility, a spokeswoman said Monday.

The request by Mohamed ElBaradei (search), director general of the International Atomic Energy Agency (search), was prompted by "a number of eyewitness and media accounts" of looting at the Tuwaitha nuclear research facility, said IAEA spokeswoman Melissa Fleming.

Accounts given by Iraqis who work at the Tuwaitha (search) site indicate "the looting continues," said Fleming.

An IAEA official, speaking on condition of anonymity, said ElBaradei had made the request despite assurances from U.S. officials that the site and its nuclear materials had been secured.

Iraq has about 1,000 sites where radioactive materials are used in industry or medicine, but the Tuwaitha facility presents by far the greatest source of concern, Fleming said in a telephone interview.

IAEA inspectors visiting Tuwaitha before the war as part of the U.N. search for weapons of mass destruction in Iraq, had catalogued tons of partially enriched and natural uranium, some believed suitable for processing into weapons-grade material.

Tuwaitha contains 1.8 tons of low-grade enriched uranium and several tons of natural and depleted uranium.

It was unclear whether any nuclear material has been stolen from the site, about 12 miles south of Baghdad.

A dispute between Washington and the U.N. nuclear watchdog on what role the IAEA should play in postwar Iraq has delayed inspections of Tuwaitha's nuclear storage depots, but U.S. troops found the door to one forced open last month.

The Tuwaitha complex was the heart of Saddam Hussein's former nuclear program and was involved in the final design of a nuclear bomb before Iraq's nuclear program was destroyed by U.N. teams after the 1991 Gulf War.

Besides concerns that material at the Tuwaitha site could be processed into nuclear warheads, experts also fear terrorists without the means of making such sophisticated arms could use it in so-called dirty bombs.

A dirty bomb is made by attaching radioactive material to a conventional explosive to disperse it over a wide area.

Searches by U.N. inspectors for nuclear, biological or chemical weapons resumed in November after a four-year pause and ended in March because of the start of the U.S.-led invasion of Iraq.

A key argument for attacking Iraq was Washington's claim that Baghdad was hiding weapons of mass destruction or programs to make them from the U.N. inspectors. While the U.S. search for evidence of such arms or programs is intensifying, Washington has resisted requests for a resumption of the U.N. inspections.

ElBaradei, in an interview with the German ZDF television network to be aired Tuesday, repeated his assertion that "there was no evidence" in the nuclear area to justify war in Iraq.

There were, however, "question marks" over whether Baghdad had destroyed biological and chemical weapons, he said.

The war was waged over the issue of weapons of mass destruction and, "we can't push it to one side just because there has been a regime change," ElBaradei said.

"I do not believe that the international community would be satisfied so long as it is not we, the U.N. weapons inspectors, who go there and examine the findings," he said.