VIENNA, Oct 12: Equipment and materials that could be used to make nuclear weapons, in some cases entire buildings housing sophisticated technology, are disappearing from Iraq, the UN nuclear watchdog has reported to the UN.

In a letter to the UN Security Council, International Atomic Energy Agency (IAEA) chief Mohamed ElBaradei said he was concerned about the "widespread and apparently systematic dismantlement that has taken place at sites previously relevant to Iraq's nuclear program" under the former government of Saddam Hussein.

A US spokesman said on Tuesday Washington would investigate the report. "Obviously we'll do a full investigation, working with the Iraqis," US Deputy Ambassador Anne Patterson told reporters at the United Nations.

Some US officials charged the report had been given to the media before Washington had a chance to see it. But UN officials said it had been sent last week to Security Council members, including the United States.

In Baghdad, a minister said UN nuclear inspectors - barred from Iraq by Washington last year - would be welcome to return if they wanted to check for the missing equipment and materials.

Released three weeks before the US presidential election, the report could fuel criticism of President George Bush, whose campaign has focused heavily on the dangers of nuclear proliferation and terrorism.

The IAEA has been warning countries to keep a close eye on all their nuclear sites due to multiple warnings from Western intelligence agencies that terrorist organizations are interested in getting their hands on a nuclear device.

The IAEA chief said in the letter that dual-use equipment - with peaceful as well as weapons-making applications - was disappearing, raising fears terrorists could be getting their hands on it.

The Oct 1 letter to the United Nations was posted on the IAEA web site on Tuesday. The IAEA, whose inspectors left Iraq before last year's invasion and have not been allowed to return, now must rely for its reporting on "open sources and commercial satellite imagery", Mr ElBaradei said.

He said "the imagery shows in many instances the dismantlement of entire buildings that housed high precision equipment (such as flow forming, milling and turning machines; electron beam welders; coordinate measurement machines) formerly monitored and tagged with IAEA seals".

Material such as high-strength aluminium has also vanished from open storage areas, Mr ElBaradei said. While some military equipment in Iraq later turned up in scrap yards abroad, "none of the high-quality dual-use equipment or materials ... (have) been found", Mr ElBaradei said.

"The disappearance of such equipment and materials may be of proliferation significance," Mr ElBaradei said. Mr ElBaradei reports every six months to the Security Council since the IAEA still has a UN mandate to investigate Iran's nuclear program.

IAEA spokesman Mark Gwozdecky said that neither US authorities in Iraq nor Iraq government officials have reported to the agency about nuclear facilities in the country.

Mr ElBaradei said in his letter that the IAEA needed "to be provided by all states with information" relevant to the agency's mandate. But Mr Gwozdecky said: "We're not getting information from authorities on what's happening."

He said that when the IAEA had inspectors in Iraq, it "had all of this stuff under close scrutiny and Iraq did regularly report to us whenever there were changes in inventory". "Iraq still has an obligation to report to us whenever there is a change in inventories, but this has not been happening," Mr Gwozdecky said. -Reuters/AFP