British Royal Marines say they have been closing in on the southern Iraqi city of Basra on Monday, after making advances overnight.
British soldiers at a checkpoint outside Basra
UK forces launched a massive offensive against Iraqi forces in the suburb of Abu al-Qassib and are now one mile from Iraq's second city.
They have also been consolidating their position in the nearby town of al-Zubayr - the second biggest in the region, with a population of about 250,000 - following what one commander called "some very brutal street fighting".
Sources told the BBC's Ben Brown, who visited the town with them, that they had used "heavy metal" - Challenger 2 tanks - to secure al-Zubayr, rather than risk infantry troops.
They may use the same tactics if they go into Basra, he said - in the hope of avoiding difficult close-combat fighting.
"Rocket-propelled grenades and machine-gun fire are just bouncing off these tanks," said our correspondent.
The marines of 40 Commando said they had secured Abu al-Qassib - a suburb with a 30,000 population - after a full day's fighting.
Hundreds of soldiers were taken prisoner, as were five senior commanders, in what one British officer described as the largest Royal Marine operation of the war so far, involving 1,000 troops.
BBC correspondent Caroline Wyatt said securing the southern suburb was significant because it meant UK forces had almost encircled the city.
She said marines described the resistance there as the toughest they had experienced so far, mainly from regular Iraqi soldiers.
Further south, on the al-Faw peninsula, a Royal Marine was killed in an Iraqi ambush, taking the UK's death toll since the conflict began to 25.
North of the city, 16th Air Assault Brigade patrolling
the Rumaila oilfields destroyed 17 Iraqi T-55 tanks, five artillery pieces and seven armoured personnel carriers, military sources said.
The British force, supported by tanks and artillery, encountered two Iraqi infantry companies - between 300 and 400 men, a number of whom have reportedly been captured.
The latest British death came in a grenade and gunfire attack on a river patrol on the southern al-Faw peninsula.
The MoD said Marine Christopher Maddison, of 539 Assault Squadron in Plymouth, was taken by helicopter to a field hospital and later died from his injuries.
The MoD also named a soldier killed in a road traffic accident in Kuwait on Sunday.
Lance Corporal SA Brierly was with the 212 Signals Squadron. Both families have been informed.
In other developments:
Two Kenyan truck drivers, kidnapped 10 days ago by Iraqis as they tried to deliver food to US troops, were freed in a British raid.
UK Defence Secretary Geoff Hoon told the House of Commons there wear no plans to send military reinforcements to the Gulf, although he maintained that some UK troops could be replaced if necessary.
He also said coalition forces had taken about 8,000 Iraqi prisoners of war, although there had so far been no
defections by senior military commanders.
Prime Minister Tony Blair is attempting to win over the Arab public by
telling a Middle Eastern newspapers that "history will judge" he made the right choice in joining the US-led war.
Focusing on the financial impact of the conflict, UK Chancellor Gordon Brown told the annual
conference of the British Chambers of Commerce that the US and Europe should not allow differences over Iraq to sour
The humanitarian situation in Basra was highlighted by Save the Children as it launched a campaign to raise £6m.
Colleagues of a Briton killed in a "friendly fire" incident on Friday described the US pilot responsible as a "cowboy on a jolly".
A Lance Corporal of Horse, Matty Hull, 25, of The Blues and Royals, Household Cavalry Regiment, died when a US A-10 tankbuster aircraft attacked a small convoy of UK tanks and armoured personnel vehicles, north of Basra.
Speaking at a briefing in Qatar, RAF Group Captain Jon Fynes said in the first 12 days of the war, 100 fixed-wing aircraft and 27 helicopters made more than 1,200 sorties and fired more than 50 Alarm missiles.