Some 15 vehicles, including a minivan and a couple of trucks, blocked the road. They were riddled with bullet holes. Some had caught fire and turned into piles of black twisted metal. Others were still burning.

Amid the wreckage I counted 12 dead civilians, lying in the road or in nearby ditches. All had been trying to leave this southern town overnight, probably for fear of being killed by US helicopter attacks and heavy artillery.

Their mistake had been to flee over a bridge that is crucial to the coalition’s supply lines and to run into a group of shell-shocked young American marines with orders to shoot anything that moved.

One man’s body was still in flames. It gave out a hissing sound. Tucked away in his breast pocket, thick wads of banknotes were turning to ashes. His savings, perhaps.

Down the road, a little girl, no older than five and dressed in a pretty orange and gold dress, lay dead in a ditch next to the body of a man who may have been her father. Half his head was missing.

Nearby, in a battered old Volga, peppered with ammunition holes, an Iraqi woman — perhaps the girl’s mother — was dead, slumped in the back seat. A US Abrams tank nicknamed Ghetto Fabulous drove past the bodies.

This was not the only family who had taken what they thought was a last chance for safety. A father, baby girl and boy lay in a shallow grave. On the bridge itself a dead Iraqi civilian lay next to the carcass of a donkey.

As I walked away, Lieutenant Matt Martin, whose third child, Isabella, was born while he was on board ship en route to the Gulf, appeared beside me.

“Did you see all that?” he asked, his eyes filled with tears. “Did you see that little baby girl? I carried her body and buried it as best I could but I had no time. It really gets to me to see children being killed like this, but we had no choice.”

Martin’s distress was in contrast to the bitter satisfaction of some of his fellow marines as they surveyed the scene. “The Iraqis are sick people and we are the chemotherapy,” said Corporal Ryan Dupre. “I am starting to hate this country. Wait till I get hold of a friggin’ Iraqi. No, I won’t get hold of one. I’ll just kill him.”

Only a few days earlier these had still been the bright-eyed small-town boys with whom I crossed the border at the start of the operation. They had rolled towards Nasiriya, a strategic city beside the Euphrates, on a mission to secure a safe supply route for troops on the way to Baghdad.

They had expected a welcome, or at least a swift surrender. Instead they had found themselves lured into a bloody battle, culminating in the worst coalition losses of the war — 16 dead, 12 wounded and two missing marines as well as five dead and 12 missing servicemen from an army convoy — and the humiliation of having prisoners paraded on Iraqi television.

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