One intelligence source in Washington said the Iraqi secret police had infiltrated the inspectors' offices in Baghdad and Mosul, and that intercepted communications proved that the Iraqis often knew in advance exactly where the inspectors planned to mount a search.
"There is very good intelligence that Iraqi intelligence has penetrated the UN compounds. There are Iraqis inside those compounds and there are microphones in there, and so before the inspectors arrive, they move the stuff out of the back door," the source said.
He said that the US also had satellite photographs of suspect sites showing Iraqi activity in advance of the inspectors' visits. However, these pictures were "not decisive" because it was not clear from them whether anything was being removed from the sites.
"Much of this stuff is smaller than the size of a sink. That's the problem. You can't see it from the air," he said.
President George Bush referred to the Iraqi attempt to thwart inspections in his state of the union speech on Tuesday night, when he said: "From intelligence sources, we know, for instance, that thousands of Iraqi security personnel are at work hiding documents and materials from the UN inspectors - sanitising inspection sites, and monitoring the inspectors themselves."
The US defence secretary, Donald Rumsfeld, would not give details of US claims but noted: "The inspectors have a difficult time arriving anywhere that is not expected, and they have a difficult time talking to anyone who hasn't been told what to say."
There is now a debate within the Bush administration about how much of this evidence the secretary of state, Colin Powell, should take with him next Wednesday when he is due to meet the UN security council in New York in an attempt to convince other member states of Saddam Hussein's bad faith, and the pointlessness of prolonging the inspections.
Making public some of the US intercepts, one US official said, would make it clear which telephones or computer communications were being intercepted.
A senior source at the security council said that Mr Powell will present material on Wednesday that the UN's chief weapons inspector, Hans Blix, has not seen before. He said the presentation was likely to relate further examples of concealment rather than actionable intelligence that would constitute a smoking gun.
The presentation may also provide evidence of other claims of Iraqi deception Mr Bush made on Tuesday night. He said: "Iraqi intelligence officers are posing as the scientists inspectors are supposed to interview. Real scientists have been coached by Iraqi officials on what to say. And intelligence sources indicate that Saddam Hussein has ordered that scientists who cooperate with UN inspectors in disarming Iraq will be killed, along with their families."
The UN monitoring, verification and inspection commission could not be reached for comment.
It is unclear what the status of Wednesday's meeting will be, diplomatic sources said. In his speech, Mr Bush said the US would ask the security council to convene and consider the facts of Iraq's ongoing defiance. Those precise words are used in the UN resolution as a precursor to a possible trigger for war.
Tony Blair yesterday threw his weight unexpectedly behind Mr Bush's claim that proven links exist between President Saddam's regime and al-Qaida, including unidentified operatives who are, his official spokesman said, being "sheltered" by the Baghdad regime.
The prime minister's assertive tone in the Commons was coupled with a warning that, once Iraq has been dealt with, North Korea and other rogue states which threaten global security will be tackled.
Choosing his words with care Mr Blair admitted that "we do not know of evidence" linking President Saddam to the attacks on September 11, but told the Conservative leader, Iain Duncan Smith: "We do know of links between al-Qaida and Iraq. We cannot be sure of the exact extent of those links."
