More than 2,000 Afghans protested outside their country's main US military base over a report that foreign troops improperly disposed of copies of the Koran and other religious items.
US helicopters fired flares to try to break up the demonstrators, some of whom were chanting anti-foreigner slogans and throwing stones.
A spokeswoman for the Parwan provincial governor said Korans were burned inside Bagram airbase, an hour's drive from capital Kabul, citing accounts from local laborers.
Top NATO general John Allen tried to contain fury over the incident, saying: "When we learned of these actions, we immediately ... stopped them ... This was NOT intentional."