More than 60,000 men from the US 3rd Infantry were poised to begin the ground war against the Republican Guard ringing the capital. Senior military sources said that Operation Iraqi Freedom’s main ground offensive would begin “within 48 hours” with an intense artillery bombardment supported by close air cover before the main body of troops stepped forward.

Preparations for an offensive that would answer the growing chorus of criticism over the conduct of the war came as new questions were raised about President Saddam Hussein’s whereabouts after he failed to make an advertised televised address. His call for jihad, urging Iraqis to rise up against the invaders, was instead delivered by the Information Minister.

The Bush Administration admitted it did not know whether Saddam was still alive. Ari Fleischer, the White House spokesman, said his failure to appear on television raised “interesting questions” and Donald Rumsfeld, the Defence Secretary, said: “Nobody knows where he is, whether he’s alive or dead.” British officials said Saddam’s non-appearance suggested that “something very serious is up”.

The allies’ main assault on the Iraqi capital is likely to start in the southwest with an initial strike to breach the Medina Division’s lines north of Karbala. Of the six Republican Guard divisions, the Medina is seen as the weakest part of Saddam’s “red line” around the capital after a week of air raids by B1, B2 and B52 bombers.

American planners are confident that the onslaught has “degraded” the Medina’s fighting strength of up to 12,000 soldiers and 400 Russian T72 tanks by at least 50 per cent.

US Central Command believes that those Medina troops who survived the airstrikes would have had little rest for seven days and no time to ready themselves for the more precise artillery barrage expected to precede wave after wave of US troops.

The largely American offensive will have air cover from RAF Harriers and Tornados and the USAF’s F15 Strike Eagles, A10 “tankbusters” and Apache attack helicopters.

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