Kabul, Afghanistan ? A suicide bombing aimed at an American military convoy triggered a chaotic round of gunfire on a busy highway in eastern Afghanistan on Sunday, leaving at least eight civilians dead and about three dozen others wounded, officials said.

The incident, which occurred outside the city of Jalalabad, set off a stone-throwing riot in which hundreds of protesters claiming that U.S. troops fired indiscriminately on civilians shouted slogans denouncing the United States and the government of President Hamid Karzai.

Afghan men shout anti-American slogans after a car bomber attacked an American convoy in eastern Afghanistan on Sunday. Following the bombing, witnesses said, U.S. troops opened fire on civilians, killing at least eight. Hundreds of Afghans gathered to protest the violence, blocking the road and throwing rocks at police.

It was the highest civilian death toll this year in an incident involving U.S. or other foreign troops. Such casualties erode public support for Karzai’s government, and the Afghan president has made repeated public appeals to allied forces to exercise greater care to avoid killing or wounding civilians.

The incident occurred as a five-vehicle U.S. convoy was on patrol near Jalalabad airfield, a large base just off a heavily traveled highway between the Pakistan border and Kabul, the Afghan capital.

U.S. military officials said American forces opened fire after a suicide attacker detonated a minivan packed with explosives as the convoy passed through the small market town of Bari Kot, whose bazaar was filled with morning shoppers.

Calling the ambush “complex,” the military said that, simultaneously with the suicide attack, U.S. troops came under small-arms fire from several directions.

Eyewitnesses, however, said the gunfire appeared to come mainly from U.S. troops whose convoy sped along the highway shooting in the direction of other vehicles and pedestrians for up to five miles from the blast scene.

Allied military officials blamed the Taliban for the civilian casualties, saying the attackers bore responsibility whether bystanders were hit by fire from U.S. troops or insurgents.