BARIKAW, Afghanistan — An explosives-rigged minivan crashed into a convoy of Marines that American officials said also came under fire from militant gunmen yesterday. As many as 10 people were killed and 34 wounded as the convoy made a frenzied escape, and injured Afghans said the Americans fired on civilian cars and pedestrians as they sped away.

American officials said militant gunfire may have killed or injured civilians, but Afghanistan’s Interior Ministry and wounded Afghans said most of the bullets were American. Hundreds of angry Afghans protested near the blast site, denouncing the American presence here.

As the Americans fled, they treated every car and person along the busy, tree-lined highway as a potential attacker, the district chief of Shinwar in eastern Afghanistan’s Nangarhar province, Mohammad Khan Katawazi, said.

“I saw them turning and firing in this direction, then turning and firing in that direction,” a 23-year-old hit by a bullet in his right shoulder, Ahmed Najib, said of the American forces. “I even saw a farmer shot by the Americans.”

Lieutenant Colonel David Accetta, the top American military spokesman in Afghanistan, said gunmen may have fired on American forces at multiple points during the escape. He said it was not yet clear how the casualties happened, though he left open the possibility that American forces had shot civilians.

“It’s not entirely clear right now if the people killed or wounded by gunfire were killed or wounded by coalition forces’ gunfire or enemy attackers’ gunfire,” he said.

The accusation that American forces killed or wounded so many Afghans was likely to cause an uproar in a country that has seen an untold number of civilians killed by international forces since the American -led invasion in 2001. A high-level delegation was appointed to investigate.

President Karzai has pleaded repeatedly for Western troops to take care not to harm civilians, and in December wept during a speech lamenting civilian deaths at the hands of foreign forces.

The American-based Human Rights Watch estimates that more than 100 Afghan civilians died as a result of NATO and coalition assaults in 2006. An AP tally, based on reports from Afghan, NATO, and coalition officials, puts the overall civilian death toll in 2006 at 834, most from militant attacks.

Nine witnesses — including five Afghans recuperating from bullet wounds in the hospital — told the Associated Press that American forces fired indiscriminately along at least a six-mile stretch of one of eastern Afghanistan’s busiest highways — a route often filled not only with cars and trucks but Afghans on foot and bicycles.

“They were firing everywhere, and they even opened fire on 14 to 15 vehicles passing on the highway,” said Tur Gul, 38, who was standing on the roadside by a gas station and was shot twice in his right hand. “They opened fire on everybody, the ones inside the vehicles and the ones on foot.”

The tolls varied. The Interior Ministry said 10 people were killed.