Amid claims that dozens of civilians had died when Coalition bombs dropped on a busy residential neighbourhood of Baghdad, both sides were getting into position for the eventual military climax of the Iraqi conflict.
An Iraqi doctor claimed more than 50 civilians were killed in an air raid which struck a busy Baghdad market late yesterday afternoon.
Dr Osama Sakhari, who was at the city's al-Noor hospital, said he had counted 55 dead and more than 47 wounded from the air strike in the Shawala neighbourhood.
The Arabic language television stations Al-Jazeera and Al-Arabiya said more victims were being sought and they showed pictures of people carrying coffins out of the hospital.
Al-Jazeera's correspondent said: "An Iraqi official told us that the search is still going on for those trapped under the rubble."
But US officials at the Central Command headquarters in Qatar told the BBC they had no details yet and suggested it may have been a misfired Iraqi missile.
"We don't have any comment on that," said Navy Lieut Commander Charles Owens. "We're still trying to learn the truth of the matter."
It is not known if there are any military installations in the area. Abu Dhabi television said the devastation may have been caused by a US cruise missile. Most of the victims were said to be women, children and older people.
A further wave of heavy bombardment hit the capital after nightfall last night, after a day of intense air attacks from US-led forces
Meanwhile, there were indications the Coalition might lay siege to the Iraqi capital rather than trying to take it in open battle in the short term.
US Defence Secretary Mr Donald Rumsfeld said Baghdad had to be isolated before it was taken. "There isn't going to be a ceasefire," he said.
Iraq's Defence Minister, Sultan Hashem Ahmad, pledged that the city would not be taken: "We will not be surprised if the enemy surrounds Baghdad in five or 10 days but he will have to take the city.
"Baghdad cannot be taken by the Americans or the Britons as long as the citizens in it are still alive," he said.
The US army's 3rd Infantry Division was 80 km south of Baghdad at Karbala while marines were advancing north between the Euphrates and Tigris rivers.
Unexpectedly strong resistance from Iraqi irregulars in southern Iraq has heightened speculation about bloody street combat in the capital in the future.
US forces who parachuted into Kurdish areas of northern Iraq were continuing their preparations for the opening of a new front.
The troop movements indicate a strategy of surrounding Baghdad with US forces just as the regime has arrayed its best-trained and best-equipped Republican Guard divisions around the capital.
US forces were last night in position to strike the Iraqi capital from nearly all sides - or to mount a siege accompanied by continuing Coalition air attacks.
US and British aircraft are targeting the estimated 30,000 Republican Guard forces spread around Baghdad as well as bombing administrative and communications centres of the regime in the city.
The bombs are getting heavier: two 4,700-pound, satellite-guided "bunker-busting" bombs were dropped from US B-2 bombers on a communications tower in central Baghdad. They were twice the size of bunker-busting bombs used previously.
British tanks and troops were continuing their attempts to secure the southern city of Basra, where the situation remained unclear.
The city was "clearly nowhere near yet in our hands", a British military spokesman, Col Chris Vernon, said.
He admitted the resolve and number of irregular Iraqi forces in the city were greater than anticipated.
Hundreds of Iraqi troops have been killed since the war began last week, the British army's Chief of General Staff, Gen Sir Michael Jackson, said. "I'm afraid they are dying in quite large numbers," he added.
Meanwhile, British military officials launched their third "friendly fire" investigation in a week, after an American A10 tankbuster aircraft shot dead one British soldier and injured five in southern Iraq.
The soldiers were on patrol in two armoured vehicles yesterday afternoon when the incident happened. Two of the injured were seriously hurt and the other three were described as walking wounded.