Iraq ? A U.S. military convoy opened fire on a column of cars Sunday morning, killing at least two Iraqi civilians in southern Iraq and igniting a new round of anger over the apparent loss of innocent life.

Key details were murky – including whether the military convoy fired as it approached the cars from behind, as local police contended. The number of fatalities was also unclear.

The incident occurred on a day when U.S. officials announced that attacks in Iraq were at their lowest levels in nearly two years.

The first word of the incident came from an apology jointly issued late Sunday by the U.S. Embassy and the U.S. military. A U.S. military spokesman said the incident was under investigation, and declined to release details. The shooting occurred near Samawa, the capital of Muthanna province, located 160 miles south of Baghdad.