Slingshots, guns fired at Afghan protest over Quran burning Shah Marai / AFP - Getty Images Afghan protesters throw stones toward U.S. soldiers standing at the gate of Bagram airbase during a protest Tuesday. Updated at 7:05 a.m. ET: KABUL -- 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. 'Very angry' A Reuters reporter at one of Bagram's gates said flares were fired from U.S. helicopters in a bid to disperse the crowd. Afghan demonstrators show copies of the Quran allegedly set alight at Bagram airbase. 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. Police said a similar protest on Tuesday just east of Kabul ended peacefully. Roshna Khalid, the provincial governor's spokeswoman, said Qurans were burned inside Bagram, citing accounts from local laborers. "The laborers normally take the garbage outside and they found the remains of Qurans," she said. 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. Public relations disaster? Allen attempted to contain fury over the incident, which could be a public relations disaster for the U.S. military as it tries to pacify the country ahead of the withdrawal of foreign combat troops in 2014. The materials recovered will be properly handled by appropriate religious authorities," said General John Allen, head of the International Security Assistance Force (ISAF), in a written statement, as well as in a video released on a U.S. military website. "This was NOT intentional in any way," his written statement said. Bagram also houses a prison for Afghans detained by American forces. The center has caused resentment among Afghans because of reports of torture and ill-treatment of suspected Taliban prisoners, with President Hamid Karzai demanding the transfer of prisoners to Afghan security. NYT: Afghan girls pay price for elders' misdeeds Allen did not provide details on the incident. Winning the hearts and minds of Afghans is critical to U.S. efforts to defeating the Taliban, but critics say Western forces often fail to grasp Afghanistan's religious and cultural sensitivities. "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," Allen added.