British forces have said taking Iraq's southern city of Basra has now become a military objective in order to get humanitarian aid to civilians there.
Iraq reports scores of civilian deaths inside Basra
The BBC's Tim Franks, who is on the Iraq-Kuwait border, says Iraq is reinforcing the city from the north and fighting there is intensifying.
On Monday, the UK's Seventh Armoured Brigade, the Desert Rats, were involved in nearly a dozen artillery engagements on the outskirts of Basra, targeting Iraqi mortars and tanks.
The United Nations has warned of a potential humanitarian crisis in Iraq's second city, which is home to 1.5 million people.
Some 100,000 children are at risk of disease as fighting there has continued for four days, disrupting supplies of drinking water, a UN spokesman said.
Engineers from the International Commitee of the Red Cross are currently working at the water pumping station with serves the city, and are hoping to restart the plant later on in the day.
Spokesman Florian Westphal told BBC News Online that no more than 40% of the city's population had access to piped water at present, and that the rest were
probably taking water direct from the river, where sewage is dumped.
Our correspondent says British commanders concede that the Iraqis are dictating the battle plan in Basra, playing their strongest suit by drawing the British into urban warfare.
He says the British wanted to handle Basra as gently as possible and hoped the people would welcome them.
But Iraqi officials say that coalition forces killed nearly 80 civilians during strikes on the city with cluster bombs at the weekend.
Iraqi reinforcements - believed to be a mix of regular troops from the 51st Division of the Iraqi army and irregular troops - have been sent into Basra from the Iraqi side from the north.
British military officials believe Iraqi fighters are placing their artillery in the middle of the civilian population.
There have been exchanges of artillery fire and television pictures have shown buildings inside the city reduced to rubble.
Correspondents say UK commanders are contemplating calling in elite paratroopers and Royal Marine Commandos after hopes of securing the city in a rapid operation faded.
In one reported incident, Royal Scots Dragoon Guards were forced to retreat about 15 kilometres (10 miles) to avoid a potential ambush by Iraqi Republican Guards believed to be heading out of Basra for a surprise attack.
UK Defence Secretary Geoff Hoon told the BBC that a balance had to be struck between the troops' safety and providing aid.
A UK naval ship loaded up in Kuwait with stocks of food, water and other supplies is still waiting to dock in the nearby Iraqi port of Umm Qasr as work continues to clear mines from the sea there.
Securing the port is seen as a crucial stage in ensuring the delivery of humanitarian aid to people in southern Iraq, and particularly in Basra.
Reports from inside the city suggest that the people there are terrified.
Leaflets and wind-up radios have been dropped from aircraft to try to reassure the population.
People have also been warned not to carry weapons on the street and advised to listen to military radio set up by the coalition forces.