"Two employees of Janusian Security were killed and a third employee is missing after anti-Iraqi forces attacked their convoy south of the Baiji Power plant... One British citizen and one Iraqi man were among those killed. A Brazilian man is considered missing," the military said on Thursday.
"They were all part of the same convoy that was ambushed."
The statement came after British firm Janusian Security Risk Management announced that a Briton and an Iraqi employee were shot dead on Wednesday near the refinery town of Baiji.
Brazilian construction company Norberto Odebrecht, which is involving in building a power plant in the region, later announced that one of its employees was probably captured close to Baiji.
Captive's identity unclear
Another foreigner was reportedly captured in the same area after an armed fighter stopped his car and killed two Iraqi police officers accompanying him, Iraqi police said.
Iraqi police said he was a Japanese engineer who worked for a power station in Baiji.
Private contractors have been
frequently targeted by fighters
But on Thursday, officials in Tokyo and at the Japanese embassy in Baghdad said they had not confirmed the report and said some information indicated the victim was not Japanese.
It was not clear whether the two attacks, which took place on Wednesday, were connected.
Private contractors have been primary targets of fighters waging a campaign against US-led forces and the interim Iraqi government.
About 200 foreigners have been abducted in Iraq since April. At least 30 foreign captives have been executed, many of them beheaded.
Aljazeera learned that a number of Iraqi and US soldiers were injured during clashes between soldiers and fighters in al-Maqdadiya area northeast of Baquba on Wednesday night.
One Iraqi and two American vehicles were damaged in the clashes.
A leader from the Jihad in the Land of Two Rivers movement was killed during the clashes.
Aljazeera also learned that US forces took over al-Salam hospital in the northern Iraqi province of Mosul to use as a military headquarters after driving out all patients and medical staff.
The seven-storey building is the city's biggest hospital.