The order comes in the wake of a US judge's dismissal of criminal charges against five Blackwater guards who were accused in the September 2007 shooting deaths of 17 Iraqis in Baghdad.
It applies to about 250 security contractors who worked for Blackwater in Iraq at the time of the incident, Interior Minister Jawad al-Bolani told The Associated Press.
Some of the guards now work for other security firms in Iraq, while others work for a Blackwater subsidiary, al-Bolani said. He said all "concerned parties" were notified of the order three days ago and now have four days left before they must leave. He did not name the companies.
Blackwater security contractors were protecting US diplomats when the guards opened fire in Nisoor Square, a busy Baghdad intersection, on September 16, 2007. Seventeen people were killed, including women and children, in a shooting that inflamed anti-American sentiment in Iraq.
"We want to turn the page," al-Bolani said. "It was a painful experience, and we would like to go forward."
Backlash from the Blackwater shooting has been felt hardest by private security contractors, who typically provide protection for diplomats, journalists and aid workers. Iraqi security forces have routinely stopped security details at checkpoints to conduct searches and question guards.
Security guards will be required within the next 10 days to register their weapons with the Ministry of Interior, al-Bolani said. Failure to do so could result in arrest, he added.
Based in Moyock, North Carolina, Blackwater is now known as Xe Services, a name change that happened after six of the security firm's guards were charged in the Nisoor Square shooting. At the time, Blackwater was the largest of the State Department's three security contractors working in Iraq.
Xe Services said the company had no employees currently in Iraq, including with its subsidiary, Presidential Airways.
"Xe does not have one, single person in Iraq," said Xe spokeswoman Stacy DeLuke.
The US Embassy in Baghdad declined comment. The State Department in Washington did not immediately respond to requests seeking comment.
The Blackwater guards involved in the incident said they were ambushed, but U.S. prosecutors and many Iraqis said they let loose an unprovoked attack on civilians using machine guns and grenades.
One of the accused guards pleaded guilty in the case, but a federal judge in Washington threw out charges against the other five in December, ruling that the Justice Department for mishandling the evidence.
The legal ruling infuriated Iraqis and Prime Minister Nouri al-Maliki vowed to seek punishment for the guards.
Last month, US Vice President Joe Biden flew to Baghdad to assure Iraqis the Obama administration to appeal the case and bring the guards back to trial.
The shooting further strained relations between the United States and Iraq, leading the parliament in Baghdad to seek new laws that would clear the way for foreign contractors to be prosecuted in Iraqi courts. The U.S. government rejected those demands in the Blackwater case.
In January 2009, the State Department informed Blackwater that it would not renew its contracts to provide security for U.S. diplomats in Iraq because of the Iraqi government's refusal to grant it an operating license.
But last September, the State Department said it temporarily extended a contract with Blackwater subsidiary Presidential Airways to provide air support for U.S. diplomats. The State Department has since ended its contracts with Xe, and DynCorp International has taken over air support.
The Justice Department now is investigating whether Blackwater tried to bribe Iraqi officials with $1 million to allow the company to keep working there after the Baghdad shooting, according to U.S. officials close to the probe.
Elsewhere in Iraq, attackers bombed an oil pipeline north of Baghdad, cutting production in half at a refinery in the capital, the Oil Ministry said Wednesday.
There were no injuries in Tuesday night's bombing in Rashidiya, just north of Baghdad.
Production at the Baghdad refinery was cut from 140,000 barrels per day to 70,000, said Oil Ministry spokesman Assem Jihad.
The pipeline runs from oil fields in northern Kirkuk province to Baghdad. It has been the target of attacks for years, and has been bombed multiple times since 2004.
