The US admits its forces lost control of security after Saddam fell

His comments were echoed by former senior US weapons inspector David Kay.

They were speaking after the UN nuclear inspectorate said items had disappeared from the sites which could have been used in nuclear programmes.

But Mr Kay said the loss was not in itself dangerous, as such materials were freely available outside Iraq.

Satellite imagery showed that entire buildings had been dismantled, said the International Atomic Energy Agency.

IAEA spokeswoman Melissa Fleming said the agency was concerned that sensitive technology might have fallen into the hands of those involved in the black market in nuclear weapons.

In comes the United States with 200,000 people on board and occupies the country in order, ostensibly, to take care of weapons of mass destruction, and they lose control... Hans Blix Iraq's nuclear puzzle

She said scrap metal from Iraqi nuclear sites, some of which was mildly radioactive, had been turning up abroad.

British Foreign Secretary Jack Straw has ordered a detailed report into the matter.

For its part, the US has said the IAEA itself had two opportunities since the war to inspect facilities and make sure materials were properly accounted for.

'No excuse'

Mr Blix said large amounts of nuclear material had been removed from Iraq - by IAEA inspectors after the 1991 Gulf War, and by the Americans when they toppled Saddam Hussein's regime and occupied the country last year.

He said Iraq still had "machines and equipment that could be of use in a nuclear programme... But of course it is not the highly-enriched uranium, or plutonium, that you need for a bomb".

However, he added: "I think what is somewhat scandalous is that it's been sitting there under an occupation. It was sitting there controlled when the inspections were there. But when the occupation comes in, it disappears...

"All these things were tagged and they were visited by the inspectors, and in comes the United States with 200,000 people on board and occupies the country in order, ostensibly, to take care of weapons of mass destruction, and they lose control and the instruments and equipment that could be helpful in nuclear production disappears."

Mr Kay said: "Exporters could export almost all of this equipment today legally, for example, to Iran without any control.

"But.. that's not an excuse for what's happened to it. Losing control of it really is inexcusable."

'Sites now secure'

The US has admitted that it shares concerns about how much and what sort of sensitive equipment and material may have disappeared in the chaos and looting which followed the invasion of Iraq.

But state department spokesman Richard Boucher said the IAEA had been allowed access to Iraq's main nuclear site, Tuwaitha, in June last year and August this year.

They had had the opportunity then, he said, to inspect facilities and make sure materials there were properly categorised and accounted for.

Iraqi Technology Minister Rashad Omar said IAEA inspectors had free access and could come back whenever they wanted.

He said that while there had been looting at the start of the US-led invasion, the sites were now secure.

The IAEA responded to Iraq's invitation by saying that any decision on the return of its inspectors would have to come from the UN Security Council.

The US removed nearly two tonnes of low-enriched uranium from Iraq earlier this year. The IAEA has verified that 550 tonnes of nuclear material still remain at Tuwaitha.

Iraq, the agency says, has asked for help to sell the nuclear material and in dismantling and decontaminating former nuclear facilities.