US troops who thought they were under attack killed an Iraqi airport employee Sunday as he drove near a military convoy on his way to work, officials said.



The driver, identified by colleagues as Baghdad International Airport worker Karim Obaid Bardan, failed to heed repeated signals to slow down or turn on his headlights as he neared the military convoy, said US and Iraqi security officials.



"As a result, the vehicle was perceived as a threat and a decision was made to engage it with small-arms fire in order to stop it and to protect the convoy from a possible attack," said Army Col. Barry Johnson, a US military spokesman in Baghdad.



"Iraqi drivers know that they must use caution and avoid threatening behavior when approaching military vehicles," Johnson said.



The shooting comes a day after Prime Minister Nouri al-Maliki said US troops would not be needed in Iraq beyond a December 2011 withdrawal deadline already in place between the two nations.



An Iraqi policeman confirmed the driver did not stop or slow. Two other Iraqi officials said the pre-dawn shooting happened near a security checkpoint on the road to the airport and described the shooting as a mistake.



All three Iraqi officials spoke on condition of anonymity because they were not authorized to brief the media.



The shooting is under US investigation, and Johnson said the military "deeply regrets" the driver's death.



Elsewhere in Baghdad, a roadside bomb in a western neighborhood killed one passer-by and wounded three during rush hour at the start of the Arab workweek. Two of the injured were policemen, according to city police and workers at Yarmouk hospital.