Guards working for an Australian-owned security company working for a company contracted by USAID fired on a car as it approached their convoy Tuesday, killing two women civilians.

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The deaths of the two Iraqi Christians — including one who used the white sedan as an unofficial taxi to raise money for her family — came a day after the Iraqi government handed U.S. officials a report demanding hefty payments and the ouster from Iraq of embattled Blackwater USA for a chaotic shooting last month that left at least 17 civilians dead.

The deaths Tuesday at a Baghdad intersection may sharpen demands to curb the expanding array of security firms in Iraq watching over diplomats, aid groups and others.

"We deeply regret this incident," said a statement from Michael Priddin, the chief operating officer of Unity Resources Group, a security company owned by Australian partners but with headquarters in Dubai in the United Arab Emirates.

RTI International, a group based in Research Triangle Park, N.C., that promotes governance projects in Iraq for the U.S. Agency for International Development, said Unity was providing security for the group but none of its staff members "were involved or present when the incident occurred."

A U.S. Embassy spokeswoman said the group was under contract by USAID but was responsible for its own security. "USAID does not direct the security arrangements of contractors," Mirembe Nantongo said.

According to the USAID Web site, RTI has about US$450 million in U.S. government contracts to work on local governance projects in Iraq.

Priddin said the company would disclose more details of the shooting after "the facts have been verified and the necessary people and authorities notified." Priddin would not comment on whether his guards killed the women.

But initial accounts — from company statements, witnesses and others — suggested the guards opened fire as the car failed to heed warnings to stop and drifted closer to the convoy near a Unity facility in central Baghdad's Karrahah district.

It was not immediately clear whether the guards were protecting a client at the time, but a group that uses its security agents said its personnel were not at the scene.

Four armored SUVs — three white and one gray — were about 100 yards from a main intersection in the Shiite-controlled district at about 1:40 p.m. As the car, a white Oldsmobile, moved into the crossroads, the Unity guards threw a smoke bomb in an apparent bid to warn the car not to come closer, said Riyadh Majid, an Iraqi policeman who saw the shooting.

Two of the Unity guards then opened fire. The woman driving the car tried to stop, but was killed along with her passenger. Two of three people in the back seat were wounded.

Priddin's statement offers a similar account: "The first information that we have is that our security team was approached at speed by a vehicle which failed to stop despite an escalation of warnings which included hand signals and a signal flare. Finally shots were fired at the vehicle and it stopped."

Iraqi police investigators said they collected 19 spent 5.56mm shell casings, ammunition commonly used by U.S. and NATO forces and most Western security organizations. The pavement was stained with blood and covered with shattered glass from the car windows.

Majid said the convoy raced away after the shooting. Iraqi police came to collect the bodies and tow the car to the local station.

A second policeman, who spoke on condition of anonymity because he feared retribution, said the guards were masked and wearing khaki uniforms. He said one of them left the vehicle and started to shoot at the car while another opened fire from the open back door of a separate SUV.

The victims were identified by relatives and police as Marou Awanis, born in 1959, and Geneva Jalal, born in 1977. Awanis' sister-in-law, Anahet Bougous, said the woman had been using her car to drive government employees to work to help raise money for her three daughters. Her husband died during heart surgery last year.

"May God take revenge on those killers," Bougous said, crying outside the police station. "Now, who is going to raise them?"

"These are innocent people killed by people who have no heart or consciousness. The Iraqi people have no value to them," said a man who was part of a group of relatives gathered with a Christian priest at the local police station.

Iraqi anger has grown against the private security companies — nearly all based in the United States, Britian and other Western countries — as symbols of the lawlessness that has ravaged their country for more than four years.

Ali al-Dabbagh, Iraq's government spokesman, said: "Today's incident is part of a series of reckless actions by some security companies."

An Iraqi investigation of the Blackwater shooting on Sept. 16 was ordered by Prime Minister Nouri Al-Maliki and called for the company to pay $8 million in compensation to the families of each of the 17 victims. The commission also said Blackwater guards had killed 21 other Iraqis in past incidents since it began protecting American diplomats in Iraq shortly after the U.S.-led invasion in 2003.

Unity also has come under scrutiny before.

In March 2006, the company issued a statement of sympathy after one of its guards was blamed for shooting a 72-year-old Iraqi-born Australian, Kays Juma, at a security checkpoint in Baghdad.

Australian Foreign Minister Alexander Downer said Juma was killed because he was in a car that failed to stop. Unity said multi-national forces and Iraqi police also were present at the checkpoint at the time.

Unity provides armed guards and security training throughout Iraq. Its heavily armed teams are Special Forces veterans from Australia, the United States, New Zealand and Britain — as well as former law enforcement officers from those countries.

In Washington, State Department spokesman Sean McCormack said the shooting did not involve U.S. diplomats. "It was not an American convoy," he said.

RTI International said Unity was fully cooperating with Iraqi and U.S. officials investigating the incident.

"We are deeply saddened by this loss of life," RTI spokesman Patrick Gibbons said in a statement. "While we have every reason to believe that proper security protocols were followed, that is a matter to be determined by the investigation."

In other violence across Iraq, at least 57 Iraqis were found dead or killed in bombings and shootings.

In Beiji, an oil hub 155 miles north of Baghdad, two suicide bombers drove a minibus laden with explosives into the house of a local police chief and detonated an explosives-packed Toyota Land Cruiser outside the home of a leading member of the local Awakening Council, a group of Iraqis who have turned against Al Qaeda in Iraq extremists in the area.

Police in Beiji said at least 19 died in the attacks, which badly damaged a Sunni mosque about 100 yards away from the police chief's house. Three guards there were among the dead. The men targeted in the attacks were not killed, police said.

In Baghdad, a series of four car bombs killed 16.