By Neil Arun BBC News Online

Cycle of violence: US helicopters over Mogadishu in 1993

In 1993, an angry crowd paraded the battered remains of an American special-forces soldier through the streets of the Somali capital, Mogadishu.

But in the 11 years since that US raid in Mogadishu ended in disaster, a telling difference has emerged - the men who died in Falluja this week were civilians, not soldiers.

They were the employees of Blackwater, one of many privately-owned firms taking over the conflict-zone security work that was once the preserve of soldiers.

Partner in war

What were they doing in Iraq?

Blackwater declined to be interviewed by BBC News Online, but a press release issued by the firm said it is "a US government subcontractor providing convoy security for food deliveries in the Falluja area".

Defence experts have described Blackwater as a formidable player in the field of private firms that serves America's security needs in the "war on terror".

Bodyguards trained by Blackwater protect the top US administrator in Iraq, Paul Bremer.

In Afghanistan, the firm's employees have provided security to countless foreign civilians involved in the post-war reconstruction effort.

'Helicopter' tower

The firm's sprawling training facility has even been used by the US military and FBI, according to former soldier John Roos, who now edits the Armed Forces Journal.

Hired muscle: Paul Bremer (far left) flanked by a bodyguard

He told BBC News Online the ranch is a soldier's dream, catering for almost every type of combat situation.

"They outfit their people with the best weapons, the best equipment," he said, describing how no expense is spared in testing new technology - often to destruction.

He offered an example of how a contract to train US coast guards in the fight against drug-smuggling led to the construction of a special tower alongside a small lake.

In training, operatives would take up positions on the tower before taking aim at a moving target on the water.

The object of the exercise, according to Mr Roos, was to simulate a helicopter raid on a boat carrying narcotics.

Flying high

Blackwater's priority, he says, is to improve its logistics - in particular, the ability to deploy its personnel at speed, anywhere in the world.

Home on the range: An entrance to Blackwater's training complex

In an interview with the Guardian newspaper in March, Blackwater Security chief Gary Jackson spoke of how the firm "has grown 300% over each of the past three years".

He also confirmed that the firm had recently recruited scores of commandos from Chile for work in Iraq.

Short-term, high-risk

Typical recruits to firms like Blackwater are elite soldiers that have retired from military special-operations units.

The risks are high, but so are the salaries, drawing in men who have seen action in hotspots around the world.

History repeated? The remains of a US soldier in Somalia, 1993

According to Mark Whyte, from UK-based company, Pilgrims Security, most of these men are not directly employed by the firms, but are rather hired as freelance "consultants".

The contracts are usually short-term and responsibility for any risks taken - and for paying taxes - rests with the individual.

Violence in the balance

According to Dr David Capitanchick, a UK-based expert, security firms are set to prosper in the current climate.

As far as governments are concerned, "mercenaries are low-risk" fighters, he said.

The public knows that, unlike regular soldiers, private guards are usually very highly paid. Faced with casualties such as the recent deaths in Falluja, said Dr Capitanchick, "people tend to say - well, that's the risk they take".

Thus as the perceived threat against foreigners working in conflict zones increases, the demand for private protection will remain healthy.

But, warns Mr Whyte, that logic too has its limits.