KABUL, Afghanistan - More than 2,000 angry Afghans, some firing guns in the air, protested on Tuesday against the improper disposal and burning of Korans and other Islamic religious materials at an American air base north of Kabul. Gen. John Allen, the U.S. commander of international troops in Afghanistan, has ordered an investigation into the incident. The demonstrators -- shouting "Die, die, foreigners!" -- started gathering in the morning after learning of the incident at the sprawling Bagram Air Field in Parwan province. As the crowd grew, so did the outrage. Ahmad Zaki Zahed, chief of the provincial council, said U.S. military officials gave him about 30 Korans and other religious books that were recovered before they were destroyed. Some are burned. Some are not burned," Zahed said, adding that the books were used by detainees once incarcerated at the base. The materials were in trash that two soldiers with the U.S.-led coalition transported in a truck late Monday night to a pit where garbage is burned on the base, according to Zahed, who spoke with five Afghans working at the pit. He said that when the workers noticed the religious books in the trash, they stopped the disposal process. Allen said he received a report overnight that "a large number of Islamic religious materials, which included Korans," had been improperly disposed of at the base. "We are thoroughly investigating the incident and are taking steps to ensure this does not ever happen again," Allen said in a statement. He offered his apologies to the president and people of Afghanistan and thanked the local Afghans "who helped us identify the error, and who worked with us to immediately take corrective action." Zia Ul Rahman, deputy provincial police chief, said between 2,000 and 2,500 protesters were demonstrating at the base. The people are very angry. The mood is very negative," Rahman said. Some are firing hunting guns in the air, but there have been no casualties. In April 2011, Afghans protesting the burning of a Koran by a Florida pastor turned deadly when gunmen in the crowd stormed a U.N. compound in the northern city of Mazar-e-Sharif and killed three staffers and four Nepalese guards.