Hundreds of Afghans staged angry protests at two sites in and around the capital Kabul, incensed by reports that NATO had site fire to copies of the Quran.
Protesters shouting "Allahu akbar, Allahu akbar" (God is great) besieged the US-run airbase in Bagram on Tuesday, firing slingshots and petrol bombs.
Guards at the base, about 60Km north of capital, Kabul, responded by firing rubber bullets from a watchtower, an AFP photographer said.
"They are demonstrating over the burning of copies of the Quran inside the base," a local official told AFP news agency.
Sidiq Siddiqi, an Afghan interior ministry spokesman, confirmed the demonstration and said reinforcements were sent to the area to prevent possible violence.
Another protest by about 500 people broke out in the Pul-e-charkhi district of Kabul not far from major NATO bases on the Jalalabad road, police spokesman Ashamat Estanakzai told AFP.
Apology
General John Allen, the US commander in Afghanistan, offered his apology and ordered an investigation into reports that troops "improperly disposed of a large number of Islamic religious materials which included Qurans".
"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," he said.
Allen's remarkably candid statement, apparently aimed at damage limitation after similar incidents led to violence and attacks on foreigners, was played repeatedly on Afghan television.
"We are thoroughly investigating the incident and are taking steps to ensure this does not ever happen again,'' Allen said.
Allegations that NATO troops working inside the base had set fire to copies of the Muslim holy book were first reported by a senior government official.
Similar protests have in the past turned violent in Afghanistan.
Some 10 people were killed and dozens of others were injured during days of unrest unleashed last April over the burning of a copy of the Noble Quran by American pastor Terry Jones in Florida.
PHOTO CAPTION
File photo of US soldiers on patrol outside Bagram airbase.
Al-Jazeera