Coalition forces resumed air attacks on Baghdad late on Saturday in what a BBC correspondent said was some of the heaviest bombing since the war began.
Iraqi civilians fear they are being targeted
Anti-aircraft fire crackled into the night as blasts hit the south-east of the city and at least two bombs struck the centre.
The Iraqi capital has been under air attack all day, with the information ministry targeted by cruise missiles in the morning.
Saturday's air strikes comes a day after a blast in a popular city market - blamed by the Iraqis on coalition bombing - reportedly killed scores of people.
The new attacks - believed to involve B-52 bombers among other hardware - are targeting units of the Republican Guard defending the Iraqi capital.
AIR CAMPAIGN TO DATE
Coalition has dropped 6,000 precision-guided bombs
US has fired 675 Tomahawk cruise missiles
Coalition warplanes have flown more than 1,000 missions
Source: Pentagon figures on 29 March
The BBC's Andrew Gilligan reports that
much larger bombs are now being used and, as night fell in the city, the rumble of explosions was almost continuous.
The top floors of the information ministry building, a base for many foreign journalists, were badly damaged by the Tomahawk missiles.
Iraqi Information Minister Mohammed Saeed al-Sahaf said the strike was aimed at stopping the world seeing television pictures of the effects of coalition bomb attacks.
Calls for revenge
Pictures of the carnage at al-Nasser market in Baghdad's Shula district have been broadcast on Arabic satellite channels throughout the Middle East.
Children have been shown in agony with blood-soaked bandages on their heads and faces.
In the hospital corridors, wailing women are seen prostrate with grief.
Iraqi hospital sources said 55 people had been killed, while Mr al-Sahaf told Lebanese television that 58 people were dead and he expected the death toll to rise.
If the number of casualties is confirmed, it would be the largest single loss of civilian life since the war began.
The BBC's Rageh Omaar reports that the market is in a part of Baghdad which is almost exclusively Shia Muslim - a religious community seen by coalition strategists as potential allies.
Our correspondents found relatives of the dead and injured demanding revenge on America and say the mood is one of extreme anger.
Iraqi officials said the market was hit by an American cruise missile but coalition spokesmen insist that a misfiring Iraqi missile could have caused the deaths.
Downing Street, citing intelligence chiefs, alleged on Saturday that Saddam Hussein had sacked the commander of Iraqi air defence because of "poor performance".
As coalition fighter planes pounded the Iraqi capital, defence officials denied calling a temporary halt to their advance on Baghdad.
There have been suggestions that the advance had been delayed because of Iraqi resistance and overstretched supply lines from Kuwait, up to 500 kilometres (300 miles) away.
Iraqi television showed three abandoned 'enemy' tanks
The BBC's David Willis, who is with US marines about 160 kilometres (100 miles) south of Baghdad, says some troops have had their rations cut to just one meal a day.
Iraqi satellite television has been showing pictures of three damaged American tanks and another vehicle abandoned near Najaf.
A presenter said the crews had fled after a confrontation with Iraqis.
American troops have been highlighting a success on the ground on Saturday with the seizure of a large arsenal in the war-torn town of Nasiriya, south of Baghdad.
The BBC's Andrew North reports that marines found enough ammunition of all kinds to supply a sizeable force for weeks.
Also at the site was what appears to be a decontamination unit and chemical weapons experts are on their way to investigate further.