The row over the shooting of Italian hostage Giuliana Sgrena by US soldiers has fuelled a debate over the rules of engagement under which they operate.
Soldiers have split-second decisions to make
The journalist was wounded by US gunfire minutes after being released from her month-long ordeal as a hostage in Iraq.
But the incident, in which a senior Italian secret service agent who had negotiated Ms Sgrena's release was killed, was just the latest in a series.
One of the worst such losses of life came in 18 January this year, when a family of seven was travelling in a car which failed to stop at a US checkpoint in the Iraqi city of Tal Afar.
US troops opened fire, killing both parents and injuring their five children sitting in the back seat.
No-one knows how many civilians have died at US checkpoints in Iraq so far.
Most are innocent people who had nothing to do with the anti-US insurgency.
And in all fairness, a considerable number of Americans and Iraqis have also died at checkpoints and convoys - all attacked by speeding cars driven by suicide bombers.
So the level of paranoia among the US soldiers is understandably high.
But the US military is irate at suggestions that its soldiers are "cowboys" who shoot first and ask questions later.
It maintains they operate under clear rules of engagement - but these rules are not readily available to the public.
US Lt Gen Ricardo Sanchez explained that the rules are meant primarily to save the lives of soldiers.
"Whenever we are engaged, or we feel there is a self-defence threat, we will respond with the necessary level of force," he said in 2003, when he commanded US troops in Iraq.
In case of an enemy attack, Gen Sanchez said, "we will bring the maximum amount of combat power that is necessary to defeat the enemy force, wherever that enemy is located."
Escalation of force
The US rules of engagement have been written with a view to being legally watertight.
And, most importantly, they are supposed to operate under the concept of the escalation of force.
This begins with careful consideration of where a checkpoint ought to be located to be sufficiently visible - and putting up signs telling people to slow down.
In Iraq, US military vehicles carry signs in Arabic warning civilians to keep away or risk deadly force. But Iraqis say not enough is done to disseminate the rules - and have asked that this be done via radio and television.
Many Iraqis cannot understand violence that leaves children injured
At the other end of the spectrum is the need for a "ceiling on operations", to ensure that US actions do not trigger a response by someone who might have been only a potential opponent.
In between lies the tragedy of many Iraqis.
In the latest incidence of "friendly fire", the car in which the Italian journalist was travelling - supposedly to safety - came under "a hail of bullets", she said, with accounts suggesting 300-400 projectiles fired.
On this occasion, the US military said:
- Troops fired on a vehicle that was approaching at high speed
- Soldiers attempted to warn the driver to stop by hand and arm signals, flashing white lights
- They then fired warning shots
- When the driver did not stop, the soldiers shot into the engine block to stop the vehicle.
In a nutshell, this would represent the textbook sequence of the gradual approach inherent in the rules.
Rules - only a guide
A Pentagon spokesman told the New York Times newspaper the rules were only a guide "to help our soldiers bear the responsibility of pulling the trigger or not".
However, there appears to be some leeway which is not always related to the split-second decisions taken by those soldiers on the ground.
The set of rules can be invoked and launched into action when forces are faced with a hostile act or hostile intent ("the threat of imminent use of force").
But it can also apply when a force or unit has been declared a hostile force, after it previously committed a hostile act or demonstrated hostile intent.
Sgrena's car was peppered with bullets
It is not entirely clear whether the last of these requirements applies in Iraq.
But officials have made it sufficiently clear that the Iraqi insurgents loyal to ousted leader Saddam Hussein and commanded, in large part, by al-Qaeda suspect Abu Musab al-Zarqawi fall into this definition.
And the US is jittery about any allegation that the rules are broken at random.
"It's absurd to make any such suggestion that our men and women in uniform would deliberately target innocent civilians," White House spokesman Scott McClellan said, rebutting Ms Sgrena's allegations that her car may have been deliberately targeted.