"The private security team initiated escalating warning procedures under the rules for the use of force, resulting in an alleged injury to a civilian occupant of the vehicle," the Corps said in a statement.
General Torhan Yusuf, Kirkuk's police chief, told AFP a female television journalist and two men were wounded in the shooting.
Sarhat Qadir, a police spokesman in Kirkuk, which is 290km north of Baghdad, said the contractors were travelling in black SUV's.
"I saw a convoy of three cars pass a taxi and one of the guards took his weapon and opened fire on the taxi," said Hussain Rashid, a police officer
"I tried myself to stop the convoy but they didn't pay attention to me."
Investigations are under way into the alleged killing of 17 Iraqi civilians last month by the US Blackwater security firm.
On October 9 two Iraqi Christian women were shot by security contractors working for Australian-owned Unity Resources Group.