(CNN) -- The security firm Blackwater USA is starting to resume normal operations in Iraq after a hiatus sparked by concerns among Iraqi and U.S. government officials over its actions.

Blackwater USA contractors secure the site of a roadside bombing in Baghdad in July 2005.

Tom Casey, a State Department spokesman, said on Friday that Blackwater and two other security firms that provide protection for U.S. diplomats in Iraq are resuming civilian convoys on a case-by-case basis.

All Blackwater USA operations in Iraq will be back to normal on Saturday, a highly placed industry source told CNN on Friday.

A deadly shooting incident on Sunday prompted the Iraqi government to bar the firm from operating. The U.S. Embassy in Baghdad has been prohibiting staff-member trips by land outside the Green Zone amid investigations into the incident.

The Iraqi government has said as many as 20 civilians were killed by gunfire from Blackwater USA contractors who were guarding a U.S. diplomatic convoy. Iraqi officials dispute the U.S. claim that the guards were responding to an attack.

The Blackwater employees involved in the incident are still in Iraq, but those who fired weapons -- about a third of the guards -- were "standing down," said State Department spokesman Sean McCormack.

Outside experts may be brought in to help review the "protective service details" in Baghdad, McCormack said. Such details usually have 15 to 20 guards.

The "full, complete review" would look at rules of engagement and overall operations, with consultation with lawyers over what authority contractors operate under, he said.

Sunday's shooting has created new tension between the U.S. and Iraqi governments. U.S. Secretary of State Condoleezza Rice expressed regret about the incident in a phone call to Iraqi Prime Minister Nuri al-Maliki and promised an open and transparent probe into what happened. Watch heavily armed private contractors at work in Iraq »

"It is extremely important to recognize we are doing important work (in Iraq). We need protection for our diplomats and I am quite certain with good will we can resolve this," Rice said.

The U.S. State Department announced Wednesday the creation of a joint commission to examine issues of security and safety in the aftermath of the shooting incident.

The commission, co-chaired by an American and an Iraqi with equal representation from both countries, will receive the results of the State Department investigation and the separate Iraqi investigation, Casey said.

The commission will look at the Sunday incident and the broader issue of "personal security details" and the use of private contractors to provide security in Iraq, he said.

The commission "is not an investigative body doing field forensics on this particular matter," Casey said. "The focus of this is to look not only at that incident but at the broader question ... and help us come up with joint recommendations."

In describing the actions of the private guards for the State Department in Iraq, McCormack said that since January 2007 there have been 1,800 movements outside the Green Zone.

"It is only a small fraction, a very small fraction, that has involved the use of force," he said.

Security duties of companies encompass certain geographic areas in Iraq: Blackwater guards State Department officials in the Baghdad region, Tricanopy operates in the south, and Dyncorp in the north. E-mail to a friend

CNN's Charley Keyes and Suzanne Simons contributed to this report.

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