The US commander of Nato troops in Afghanistan has apologised over reports that foreign troops had "improperly disposed" of copies of the Koran.
In a statement General John R Allen ordered a full investigation.
"When we learned of these actions, we immediately intervened and stopped them," he said.
Reports of the alleged Koran burning have led to a large protest outside the US air base at Bagram outside Kabul.
Police told the BBC that about 3,000 people were taking part in the demonstration and that some elders have gone into the base to talk to Nato officials.
The Pakistan-based Afghan Islamic Press news agency has reported that the protesters have started a bonfire in front of the airfield.
In his statement, Gen Allen said that the investigation would examine whether troops at Bagram air base "improperly disposed of a large number of Islamic religious materials which included Korans".
"The materials recovered will be properly handled by appropriate religious authorities," the statement said.
"We are thoroughly investigating the incident and we are taking steps to ensure this does not ever happen again. I assure you… I promise you … this was not intentional in any way."
Gen Allen went to offer his "sincere apologies for any offence this may have caused", including to the president of Afghanistan, the Afghan government and "the noble people of Afghanistan".
In April last year at least one person was killed and 18 injured in successive days of protests in Afghanistan over the burning of a Koran in the US.----
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