"We are putting in place more robust assets to make sure that the management reporting and accountability function works as best as it possibly can," Sean McCormack, state department spokesman, said on Friday.

US authorities will also record all of the company's radio transmissions and begin archiving electronic tracking and movement data.

"The idea here is if you have an incident, you have a record," McCormack said.

The new measures will apply only to Blackwater and not to two other state department security contractors in Iraq, Triple Canopy and SynCorp.

Oversight activities

Marwan Bishara, Al Jazeera's senior political analyst, said that anger in Iraq and the United States had forced the state department to come up with the new controls but their effect would be limited.

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"These kinds of very light, logistical, technical oversight activities will simply legitimise the US presence in Iraq in terms of private contractors and mercenaries," he said.

There are four different ongoing investigations into the September 16 shooting which Blackwater maintains was in response to an ambush.

Witnesses have accused them of firing indiscriminately into a crowded square.

"These [measures] are not meant to signal that the review or the investigation of the 16 September incident is heading in any particular direction," McCormack said. 

'Obviously wrong'

A senior US military official reportedly told the Washington Post newspaper on Friday that the guards involved in the shootout were "obviously wrong".

"The civilians that were fired upon, they didn't have any weapons to fire back at them. And none of the IP [Iraqi police] or any of the local security forces fired back at them," the unnamed official was quoted as saying.

Blackwater, which has earned more than $1bn from US government contracts since 2001, has defended its work in Iraq and says it acted "appropriately" during the incident.

Erik Prince, Blackwater's founder, said in remarks prepared for a congressional hearing earlier this week that his men came under small-arms fire and "returned fire at threatening targets".

Nuri al-Maliki, the Iraqi prme minister, has said that Blackwater should leave the country because of an "abundance of evidence" against the contractor.