As many as 20,000 private security contractors are working in Iraq

The Iraqi government said it wanted to determine whether such contractors were operating in compliance with Iraqi law.

The review comes a day after the Iraqi authorities ordered the US-based firm, Blackwater USA, to suspend all operations and leave Iraq immediately.

Blackwater has said its guards acted in self-defence in Sunday's incident.

But the Iraqi interior ministry has claimed the men fired "randomly at citizens" in a crowded square in the capital, killing innocent bystanders and a policeman.

The Blackwater guards were protecting a convoy carrying officials from the US state department at the time.

Unclear status

The Iraqi government's spokesman, Ali al-Dabbagh, said its decision to review the status of Private Security Companies (PSCs) was prompted by the "flagrant assault... on Iraqi citizens" on Sunday.

BLACKWATER USA FACTS Founded in 1997 by a former US Navy SEAL Headquarters in North Carolina One of at least 28 Private Security Companies in Iraq Employs 744 US citizens, 231 third-country nationals, and 12 Iraqis to protect US state department in Iraq (May 2007) Provided protection for former CPA head Paul Bremer Four employees killed by mob in Falluja in March 2004 Personnel have no combat immunity under international law if they engage in hostilities

Profile: Blackwater USA

"Companies should respect Iraqi laws and the dignity of the citizens," he added.

The BBC's Hugh Sykes in Baghdad says the status of the thousands of often heavily armed private security guards employed in Iraq is unclear.

The guards are considered neither civilians nor military personnel, although they do carry IDs from the US Department of Defense.

Order 17 of the Coalition Provisional Authority gives the guards immunity from Iraqi prosecution, but they have no combat immunity under international law if they engage in hostilities.

Any Iraqi review of their status would therefore only have an effect if the US authorities accept its conclusions, our correspondent says.

'Fair probe'

Earlier, the US Secretary of State, Condoleezza Rice, telephoned Prime Minister Nouri Maliki to express her regret over the deaths and pledge to help carry out a "fair and transparent" investigation into the incident.

A spokesman for Ms Rice told the AFP news agency that she had "reiterated that the United States does everything it can to avoid such loss of life in contrast to the enemies of the Iraqi people who deliberately target civilians".

The two agreed to hold any wrongdoers accountable, according to Mr Maliki's spokesman.

Blackwater is one of the biggest private security contractors in Iraq and is reported to have a contract worth $300m (£150m) with the state department to protect its diplomatic staff and equipment there.

Last week, the US ambassador to Iraq, Ryan Crocker, spoke of the importance of private security contractors in Iraq and correspondents say their suspension would be a potentially serious blow to the state department's work there.