A half-dozen armored sport utility vehicles with guns pointed out the windows careen onto Baghdad's busy airport highway, bringing traffic to a screeching halt.
Iraqis have learned to keep a wary distance from the convoys of foreign guns-for-hire in mirrored sunglasses and bulletproof vests, who have a reputation of firing at any vehicle that gets too close because of the ever-present danger of suicide bombers.
Iraqi officials accuse many of the companies providing protection in violence-plagued Iraq of being a law unto themselves, prompting a flurry of attempts to better regulate an industry that is expanding rapidly around the world.
South Africa and Britain are proposing tough new laws governing the participation of their nationals in foreign conflicts. Humanitarian groups are trying to identify gaps in international law. And the industry itself is pushing greater self-regulation.
Iraqi Interior Minister Bayan Jabr, who oversees the activities of private security companies, accuses them of being "militias." Some companies counter that Jabr, who has himself been linked to a private Shiite force accused of widespread abuses against Sunni Muslims, is contributing to the problem by refusing to register security contractors.
Since militaries were slashed at the end of the Cold War, private companies have been a growing presence on the world's battlefields, performing jobs conventional forces can no longer handle. It is a hugely competitive, multibillion-dollar industry, with clients ranging from governments and blue-chip corporations to warlords, drug cartels and terror groups.
In Iraq, at least 20,000 contractors -- local and foreign -- are guarding coalition bases, protecting US officials, training Iraqi security forces and interrogating detainees. They also protect businessmen, journalists and humanitarian workers, among others.
Doug Brooks, head of a US-based association of military contractors, says reports of abuse in the industry are exaggerated.
"In general, companies are using people who are middle-aged ex-military, so they know what they are doing, and they don't make as many mistakes" as the armed forces, he said.
The companies say they recognize the need for regulation in a dangerous industry.
"We would prefer a high level of professionalism across the board. It makes it easier and safer for everybody," said Greg Lagana, spokesman for US-based DynCorp International.
Many top firms have joined associations like Brooks' International Peace Operations Association, which impose stringent human-rights standards on their members. Firms say they also are subject to volumes of legislation.