A series of explosions shook Baghdad during the morning as the southern, western and northwestern outskirts came under new waves of bombing, an AFP correspondent reported.

The bombardments hit as a US military spokesman said American forces were attacking four elite Republican Guard divisions around Baghdad, in what one officer called the "last push" toward the Iraqi capital.

A spokesman with the US Central Command told AFP the Baghdad, Medina and Nebuchadnezzar divisions were being engaged by American troops south of the capital, while the Adnan division was being pounded from the air to the north.

The battle for Baghdad appeared to be starting in earnest as US troops crossed through a 3,000-meter (yard) wide desert strip known as the Karbala Gap, a major gateway toward the capital, in their drive to topple the Iraqi president.

"This is it, the last push," said Major Maurice Goins before the advance near the Shiite Muslim holy city of Karbala, some 80 kilometers (50 miles) south of Baghdad.

Elements of the Guard's Medina armoured division and other units had earlier been reported lying in wait in the area but apparently failed to engage in combat.

Saddam's main presidential compound in the city had come under intensive attack from coalition bombs before dawn, as it had for the previous two days.

The latest attack on the riverside Republican Palace occurred at 3:05 am (0005 GMT), 10 minutes after a bridge in the east of the city was targeted.

Saddam's call to arms was read on state television on night 13 of the war to topple him from power, in an appeal to stoke international fury over the latest killings of women and children.

But US President George W. Bush blamed Saddam for civilian deaths, as US and British forces continued both the air blitz and a grinding, bitterly fought ground campaign pushing northward towards a showdown in Baghdad.

In a speech read by Information Minister Mohammed Said al-Sahhaf, Saddam said jihad was a "duty" for Arabs and Muslims and branded the US-led war an assault on "religion, property, people and honour".

"Fight them in every location as you are doing today, and don't give them a chance to catch their breath until they pull out of Muslim land," the speech said. "Hit them, fight them! They are evil aggressors."

Saddam hit out again Wednesday in a new message read out in his name on Iraqi satellite TV, warning Iraq had so far committed only "a third" of its armed forces in the conflict.

"The opportunity is there today to defend religion, honour and principles in the face of the invaders," said the message, dated April 1 and read out by a presenter in military uniform.

US commanders say they do not know if Saddam, who has almost always steered clear of live television during his 24-year rule, remains alive after the thousands of air strikes which have pounded Iraq since March 20.

Both London and Washington said Saddam's non-appearance on television raised "questions" about his fate.

Iraqi officials have scorned any suggestion he may be dead or hurt, while state television regularly shows him meeting with his inner circle. But it is never known if such footage is pre-recorded.

The rallying cry came after at least 48 more civilians, many women and children, were reported dead in the round-the-clock aerial assault that has been pummelling Baghdad and surrounding areas.

In the farming town of Hilla south of the capital, the local hospital director said 33 people were killed and more than 300 wounded in a bombing raid Tuesday.

A spokesman for the International Committee of the Red Cross described the "horror" at the hospital and said: "There were dozens of smashed corpses."

An AFP reporter saw what appeared to be the component devices from cluster bombs, equipped with small parachutes, covering a large area in the town, which lies 80 kilometres (50 miles) south of Baghdad.

Another AFP reporter with US ground troops assaulting the area said the attack had been backed up by air raids from B-52 bombers.

US Central Command said it was investigating the report but "has not turned up any evidence of this alleged incident."

The images of civilian carnage have played over and over on Arab television stations, and press reports in the United States about internal dissent over how to prosecute the war have proved a public relations headache for Washington.

SPACE.WIRE