The rules are blurred in Iraq in ways never seen before. It might be called the first privatised war of modern times.
By Stephen Evans
BBC North America business correspondent
Do Geneva Conventions protect contractors?
One academic study says the ratio of private contractors to US military personnel in the Gulf now is roughly one to ten, ten times the ratio during the 1991 war.
In Abu Ghraib prison - where contractors are reported to have run interrogations - that means unclear lines of legal responsibility.
The Red Cross is also worried about similar blurring right across the conflict because of the growth of private contractors.
Claude Voillat, the Red Cross' deputy head of operations in the near east, says some private security personnel do not have the training to deal with tense situations on the streets.
"Our concern is that there is a void of regulation; a void in terms of rules of engagement that may become a real danger once you put some of these people with a gun in the field.".
The Red Cross fears that private soldiers who breach international conventions might not be accountable, so it plans to get governments to hold companies to account.
"This is the main point to put back the responsibility to the governments," says Mr Voillat. "Should it be the government who hires the company or the government where the company comes from?"
People on the ground in Iraq say most companies are responsible.
There are old established firms but such is the scale of expansion now that new companies are being set up, according to one former soldier involved in special operations who is now in Iraq with a security company.
Private guards watch over the US's man in Iraq Paul Bremer (far left)
Where the older firms relied on top, ex-military people, the new ones do not.
"They are not all going to have a blue-blood, special forces background and indeed there are many, as we say, Walter Mittys," said the soldier.
"The vetting process is pretty poor," he said, "because a lot of these companies are put together very quickly to react to a contract."
The danger is that fierce competition for lucrative contracts results in corners being cut.
Whose law applies?
Armour Group has been in business for 20 years. It is currently working for the Pentagon in Iraq.
A lack of clarity may have helped governments in the past. Private companies might be able to do things government forces found unacceptable and deniable
Christopher Beese, who runs the company, wants clearer rules.
"There are some who've only been in business for a year or two.
"They have had perhaps insufficient time to produce the necessary policies, procedures and safeguards to ensure that their people are properly selected and there is therefore considerable difference between the newcomers, if you like, and those who've been in the business some time."
So Iraq is a mix of new and old companies, of private and public security people, all working to different employers and different rules in an unclear legal framework.
A British company may contract to the American government, so whose law then applies - British, Iraqi or American?
Do the Geneva Conventions protect private employees if they are captured?
Call for clarity
Peter Singer of the Brookings Institution in Washington, the authority in the field, says clarification is essential.
"There's no international law that controls this industry right now - that's a gap that needs to be filled."
"The second is that the clients in this industry - mainly in the US - need to re-evaluate what roles are appropriate to outsource and what roles are simply too important to the public interest to hand over to the private market."
A lack of clarity may have helped governments in the past.
Private companies might be able to do things government forces found unacceptable and deniable.
In Iraq though, it is not obvious that the absence of clear regulation is helping the coalition cause.