Coalition troops "accidentally killed" two Afghan civilians and injured one "during a firefight with insurgents" last week, NATO's International Security Assistance Force said Tuesday.
That conclusion was reached after an assessment of the Thursday incident by the Afghan and ISAF military, it said.
The flare-up occurred in Helmand province's Nahr-e Saraj district.
The unit was ambushed while traveling between two forward operating bases and returned fire at a van they thought was part of the attack.
"During an ambush, a vehicle approached the ISAF convoy at a high rate of speed," an ISAF statement said.
"After determining the vehicle was a potential threat and wouldn't stop, coalition forces reacted by using appropriate escalation of force procedures to protect members."
Civilian deaths in warfare have undermined the credibility of international forces in Afghanistan, and ISAF has been working to avoid them.
– CNN's Joe Sterling contributed to this report