American soldiers who shot and killed an Italian intelligence officer in a friendly fire incident in Baghdad (search) generally followed instructions for dealing with potential threats, a U.S. investigation is expected to conclude.

But the probe into the March 4 shooting is also expected to raise concerns about the rules of engagement at a Baghdad checkpoint, a senior U.S. defense official said Monday. The official spoke on condition of anonymity because the report has not been finished.

It was unclear whether the Italians who took part in the investigation would endorse the report, the official said.

According to Italian news reports, they disagreed with the U.S. findings and were refusing to sign it. Ben Duffy (search), a U.S. Embassy spokesman in Rome, said the United States was still hoping for a combined report.

The rules of engagement direct soldiers to use warnings, then deadly force, against potential threats as they approach, and are designed to avoid mistaken shootings while also protecting soldiers from homicide bombers.

The U.S. official left open whether soldiers at the temporary checkpoint during the shooting could face criticism for their performance. However, a conclusion that they followed orders would make it less likely they would be accused of making significant mistakes.

The Italians' refusal to endorse the conclusions would hurt the report's credibility in Italy, which sent 3,000 troops to Iraq after the U.S.-led invasion.

The Italian officer, Nicola Calipari, died trying to shield a hostage he had just helped free from her insurgent captors. He was killed when U.S. soldiers at the checkpoint fired on his car as it approached them. The hostage and an Italian officer who was driving were wounded.

From the first hours after the shooting, Rome and Washington have differed over what led to the killing.

Soldiers at the checkpoint said the car was speeding toward the checkpoint and the driver ignored warnings to stop. According to the U.S. 3rd Infantry Division, the soldiers "attempted to warn the driver to stop by hand and arm signals, flashing white lights, and firing warning shots in front of the car."

"When the driver didn't stop, the soldiers shot into the engine block which stopped the vehicle, killing one and wounding two others," it said.

The driver and the ex-hostage, journalist Giuliana Sgrena (search), have insisted the car wasn't speeding and that the soldiers gave no warning. At the time of the shooting, they were driving to the Baghdad airport after negotiations led to Sgrena's release.

The senior U.S. defense official declined to describe any determinations the investigation has made about the car's speed and other disputed issues.

Another issue is to what degree, if any, the Italians coordinated their rescue operation with U.S. forces in the area.

In the days after the shooting, the top U.S. general in Iraq, Gen. George Casey, ordered a review of violent incidents at checkpoints to avoid any future mistakes. The shooting took place just a few days after a Bulgarian soldier was killed in a possible friendly fire shooting at another checkpoint in Iraq.

Italian Premier Silvio Berlusconi (search), a staunch U.S. ally, faces strong opposition at home to his decision to send troops to Iraq after the U.S.-led invasion. Pressure to pull out the troops mounted after the death of Calipari, who is now a hero in Italy.