The Iraqi capital, Baghdad, has come under one of the most intensive aerial bombardments by coalition forces since the start of the war against Saddam Hussein.
Buildings shook as bombs hammered Baghdad
Correspondents say air raids are going on day and night now, with apparently heavier and heavier munitions.
Massive explosions were heard from around the southern outskirts of Baghdad, where the United States is trying to displace units of the Republican Guard, at about 1600 local time (1300 GMT).
In the south, from where the American assault on Baghdad is most likely to come, US troops have been digging in, ringing their positions with foxholes and artillery pieces to defend them while they wait for the order to move forward.
In other developments:
- Fifteen people are injured after a truck drives into a group of American soldiers outside a shop at Udairi Camp military base in Kuwait
- Iraqi Information Minister Mohammed Saeed al-Sahaf says Iraq has shot down two US helicopters; the Pentagon denied the claim
- British forces say they have captured five Iraqi officers and an Iraqi general, and killed a Republican Guard colonel, in clashes south of Basra
- A US magazine says Defence Secretary Donald Rumsfeld overruled his military chiefs, insisting the US went to war in Iraq with a relatively small and lightly armed force
- US forces say they have seized a large arsenal in the central town of Nasiriya, with an apparent decontamination unit found along with several weeks' supply of ammunition
- UK pilots say they have destroyed a fuel depot used to supply Republican Guard tanks near Karbala
- Al-Jazeera television reports fresh air strikes on Basra and Mosul
- US Central Command in Qatar says two more marines have been killed in accidents in southern Iraq
Huge explosions have rocked the capital almost non-stop since Saturday night, when bombs struck a training site for Fedayeen paramilitaries loyal to Saddam Hussein, and a palace believed to belong to the Iraqi leader's son, Qusay.
Our correspondent there says the skies are dark with smoke from burning oil-filled trenches meant to obscure the city to incoming bombs and missiles.
The US war commander, General Tommy Franks, rejected suggestions coalition forces had implemented a pause in the fighting because of overstretched supply lines and formidable Iraqi resistance.
"[Combat operations] are continuing in the north, they're continuing in the west, they're continuing right around Baghdad," he told a news conference at US Central Command in Qatar.
The BBC's Michael Voss, who is in Qatar, says while there officially is no pause, there is nonetheless a realisation that this could turn into a protracted war and the focus now is on securing supply lines.
He says that on the ground, the first signs of a tactical shift by military commanders appear to be taking shape.
General Richard Myers, the head of the US Joint Chiefs of Staff, said coalition forces could afford to be patient.
"With the outcome never in doubt, we can afford to take our time and set the conditions on the battlefield," he told BBC television.
In another development, the UK Government said the head of Baghdad's air defences has been sacked because Iraq's own missiles have been falling on the capital.
Correspondents say this is one possible explanation being put forward by the coalition for two devastating explosions at Baghdad markets on Wednesday and Friday in which dozens of people died.
There has been no confirmation of the report from the Iraqi side.
US commanders have been reviewing procedures after the loss of four soldiers from the 3rd Infantry Division in a suicide bombing near the central town of Najaf on Saturday.
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
General Myers said: "I think we can adjust our tactics and techniques to overcome that threat [of suicide bombers]."
The attack was the first suicide bombing of the war, but Iraqi Vice-President Taha Yassin Ramadan warned: "This is just the beginning."
He added: "It will be routine military policy. We will use any means to kill our enemy in our land and we will follow the enemy into its land."