Afghan demonstrators used slingshots and fired guns in the air while U.S. helicopters responded with flares, after thousands of angry people gathered Tuesday to protest the alleged burning of copies of the Quran at the main U.S. military base in Afghanistan.

The demonstrators — shouting “Die, die, foreigners!” — started gathering in the morning after learning of the incident.

The top NATO general in Afghanistan, General John Allen, ordered an investigation, offered “sincere apologies”  and said any improper handling of the Quran was “NOT intentional” in a written statement.

Photographs taken by the AFP news agency outside the Bagram airbase, an hour’s drive north of the capital Kabul, showed people firing sling shots and others holding charred copies of the Quran, Islam’s holy book.

“There are about 2,000 to 3,000 demonstrators, throwing stones at the base and chanting down with the foreigners,” Rahman Sayedkhili, a senior police officer in Parwan province, where Bagram is located, said.

A Reuters reporter at one of Bagram’s gates said flares were fired from U.S. helicopters in a bid to disperse the crowd.

“The people are very angry. The mood is very negative,” Zia Ul Rahman, deputy provincial police chief, said. “Some are firing hunting guns in the air, but there have been no casualties.”

Ahmad Zaki Zahed, chief of the provincial council, said U.S. military officials gave him about 30 Qurans 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.

General John Allen said “This was NOT intentional in any way,” he went on to say
“I offer my sincere apologies for any offence this may have caused, to the president of Afghanistan, the government of the Islamic Republic of Afghanistan, and most importantly, to the noble people of Afghanistan.”