Mr Rumsfeld said that disclosing such details to the world or even to the United Nations Security Council could jeopardise any military mission by revealing to Baghdad what the United States knows.

When weighing the demands of global opinion for proof of President Saddam Hussein’s danger against the need to shroud an effective military campaign in secrecy, Mr Rumsfeld said the safer option would be for the US to tilt towards secrecy.

He said that the final decision on the pros and cons of revealing sensitive intelligence material would be Mr Bush’s, but he added: “To the extent that prior to using force he were to reveal intelligence information in a way that damaged the ability to conduct the conflict, it would be, needless to say, unfortunately, risky for the coalition forces’ lives engaged.

“And I don’t know what calibration would be made there. On the one hand, you have the advantage of persuading the publics in the world and countries of the facts of the matter, and on the other hand, by so doing, you weaken your ability to do that which you have decided to do.”

His remarks are likely to unsettle potential US allies and complicate the task of assembling a diverse coalition for any attack on Baghdad.

Moderate Arab states have said that any military action would need the authorisation of the UN if they are to open their military bases and airspace to the US and British military. But the prospects of a second UN resolution, to follow the 15-0 vote that authorised the present inspection regime in Iraq, would be hampered if the US was unwilling to share its intelligence.

With the US military build-up continuing apace, American officials disagree with Jack Straw, the Foreign Secretary, that the chances of war are receding. One said that the time for conflict was approaching “sooner rather than later”.

Downing Street has indicated that it would prefer a second UN resolution before starting military strikes. But the prospect of a speedy vote is unlikely, partly because of the five incoming members who will change the dynamics of the 15-member body.

Spain, Germany, Angola, Chile and Pakistan have taken over five of the ten rotating seats from Colombia, Ireland, Mauritius, Norway and Singapore. The incomers are regarded as posing tougher nuts to crack for American negotiators at the UN than those they are replacing. Gerhard Schröder, the German Chancellor, made his opposition to an Iraq war the centrepiece of his re-election campaign, although he has recently tempered his rhetoric and is trying to mend fences with Washington.

Hans Blix, the UN’s chief weapons inspector, and Mohamed El Baradei, head of the International Atomic Energy Agency, will today give the Security Council an interim briefing on Iraq’s 12,000-page weapons declaration, which is likely to highlight its shortcomings and omissions. They will return for the critical meeting on January 27, at which they will give their assessment of Iraq’s compliance.

Washington and London insist that the meeting should not be regarded as a trigger for war, although their emphasis is subtly but crucially different. Mr Straw has said that the inspectors should be given time to continue their searches, which have apparently turned up little so far, but the White House insists that the date is no trigger because so much is already known about Saddam’s breaches of UN resolutions.

UN inspectors used helicopters for the first time this week and searched at least eight sites yesterday. One site, the al-Tareq public company 55 miles northwest of Baghdad, was a chlorine plant, according to Iraqi officials there. Inspectors, who have visited the site six times in recent weeks, took samples during a four-hour stay.

Explore World News

• Iraq News

• US & Americas News

• Europe News

• Middle East News

• Asia News

• Africa News

Times Recommends

• Valley of death may be $88bn key to life
• Hope fades for the missing as earthquake toll leaps
• Invasion of the alien computer-eating ants