A crowd of up to 2,000 demonstrators gathered outside the main U.S. military base in Afghanistan Tuesday, following reports that foreign troops inside the facility had improperly disposed copies of the Quran.

The commander of the international coalition, U.S. General John Allen, quickly apologized and promised an investigation after learning that coalition forces at Bagram Airbase may have “improperly disposed” of a large number of Islamic religious texts, including the Quran.

Allen insists the incident was not intentional, and said NATO is taking steps to make sure that this “does not ever happen again.” He said the texts have been given to religious authorities to be “properly handled.”

There were no immediate reports of violence during the protests to denounce the alleged desecration. Afghan protests against the destruction of the Muslim holy book have turned deadly in recent years.

In April 2011, about 20 people were killed during several days of protests across Afghanistan after little-known U.S. pastor Terry Jones burned a Quran at his small Florida church.