Hundreds of locals reportedly gathered to protest the killings, which took place near the eastern city of Jalalabad.
A spokesman for the Nangarhar Province governor's office told AP that some Afghans were killed or wounded after U.S. soldiers opened fire after the bombing.
A U.S. military spokesman, Major William Mitchell, described the initial attack as a "complex ambush" that involved militants firing on the convoy from three different points.
"We certainly believe it's possible that the incoming fire from the ambush was wholly or partly responsible for the civilian casualties," AP quoted Mitchell as saying.
The U.S. soldiers were part of the U.S.-led coalition and not NATO's International Security Assistance Force, according to the agency. One U.S. soldier was reported injured.
AP also reported that U.S. soldiers deleted photographs taken at the scene by a freelance photographer working for the news agency. Video shot by a second freelancer working for AP Television News was also reportedly deleted. Neither of the freelancers had witnessed the initial suicide attack or the ensuing gunfire. The U.S. military did not immediately comment on the matter, according to the agency.
Meanwhile, the NATO-led International Security Assistance Force said two of its soldiers were killed in combat in southern Afghanistan on March 3.
It did not identify the nationalities of the soldiers or say where the violence happened.
(Reuters, AFP, AP)