BAGHDAD, July 28 (Reuters) - The U.S. military said an investigation into an incident in which American troops killed three Iraqis near Baghdad airport last month showed the victims were not criminals but innocent civilians.

In a statement released at the time of the June 25 incident, the military said troops fired at a car near the airport after coming under attack. It called the three people inside the vehicle "criminals", adding a weapon had been found in the car.

"A thorough investigation determined that the driver and passengers were law abiding citizens of Iraq," the military said in a statement released late on Sunday.

No weapon was found in the vehicle, it added.

The statement also said troops involved in the incident were not at fault.

A man and two women were killed in the shooting, local officials said at the time.

The result of the investigation comes at a sensitive time for Washington, which is negotiating a new security deal with Baghdad to govern the presence of U.S. troops in Iraq when a U.N. mandate expires at the end of the year.

The investigation also follows other recent shootings involving U.S. troops that have infuriated Iraqi officials.

"This was an extremely unfortunate and tragic incident," said Colonel Allen Batschelet, chief of staff for U.S. troops in Baghdad.

"We are taking several corrective measures to amend and eliminate the possibility of such situations happening in the future."

The military statement on the results of the probe said a convoy travelling near Baghdad airport pulled off to the side of the road when one vehicle experienced problems on June 25.

While the vehicle was being checked, a civilian car approached at what soldiers believed was high speed, the statement said.

"Soldiers perceived the rapidly approaching vehicle as a threat and executed established escalation of force measures. When the vehicle failed to respond to the soldiers' warning measures, it was engaged with small arms fire," the statement added.

It said the initial statement of a weapon being found resulted from a misunderstanding that the Iraqi Police arriving at the scene had collected a weapon.

In late June, U.S. troops on a raid near the holy Shi'ite city of Kerbala shot dead a man that some officials said was a distant relative of Prime Minister Nuri al-Maliki.

The military at the time said that incident was under investigation and expressed "deep regret" at the loss of life.

In mid-July, U.S. forces shot dead the 17-year-old son and another relative of the governor of northern Salahuddin province in a raid, local officials said.

The U.S. military said it shot two armed men, adding it was later found they were both related to the governor.