“The offensive is from north to south,” the officer says, describing the assault on the Sunni Muslim bastion that started Monday evening.

The officer says the force faced initial resistance which has since ceased. About 12,000 US and Iraqi forces are taking part in the offensive.

US-led forces adopted a strategy of penetrating the city on the ground from the northwestern Jolan neighbourhood and the Askari district in the northeast. It was here where forces took control of Fallujah’s railway station overnight, about four or five kilometres from a central road that slices Fallujah from east to west.

At the same time the military battered the centre of the besieged enclave with a barrage of artillery and aerial fire.

Fearful of roadside bombs as they advanced into the notorious Jolan sector, US marines smashed through a railway line and ploughed through fields.

Knocking down walls, they moved house-to-house through the Jolan neighbourhood, seen as the heart of rebel activity in Fallujah, spraying rounds of machine gunfire at buildings from where militants fought back with mortars.

Asked whether troops had taken control of Jolan, the high-ranking official said “pretty much.”

The onslaught was unleashed after Iraq’s interim Prime Minister Iyad Allawi announced he had given the permission for the military to retake the city.

Fallujah has become the symbol of a potent insurgency that is bent on undermining his US-backed interim government, as well as being the suspected home base of militants such as Musab al-Zarqawi, whose followers have been behind some of the Iraq’s deadliest attacks.

US Defence Secretary Donald Rumsfeld indicated that US and Iraqi forces would seek a decisive victory over insurgents in Fallujah, leaving no more room for a negotiated settlement.

In April, US marines withdrew from Fallujah after an assault on the city and reports of heavy civilian casualties sparked widespread resistance in Iraq and condemnation in the Arab world.

US commanders estimate that 2,000 to 2,500 fighters, some loyal to Mr al-Zarqawi, are inside the city and its surrounding areas, ready to fight. The military believes that another 10,000 men could join in the battle.

Up to 90 per cent of Fallujah’s 300,000-strong population is thought to have fled the city before the assault began.