Kabul, Afghanistan (CNN) -- The recent burning of Qurans at a NATO base in Afghanistan involved five American servicemen and a local translator, according to a NATO official familiar with the investigations.
The Qurans burned were among religious materials seized from a detainee facility at Bagram Airfield last week.
Throngs of outraged Afghans took to the streets following the incident, prompting U.S. President Barack Obama to apologize to his Afghan counterpart, Hamid Karzai, calling the burning an inadvertent error.
Furor over the burnings have fueled a string of protests and attacks that have left at least 39 people dead, including four American soldiers. Hundreds more have been wounded in the attacks.
A man wearing an Afghan National Army uniform killed two U.S. soldiers last week at a base in eastern Afghanistan. Last weekend, two senior U.S. officers were gunned down inside the heavily secure Afghan Interior Ministry when a junior intelligence officer turned his gun on them.
A suicide bombing Monday at a military airfield in eastern Afghanistan killed nine people and wounded 12, Afghan police said.
Afghan officials have suggested the attacks are in response to the Quran burning.
Afghan and NATO officials are investigating the incident, and the latter said a decision on what to do about the burning will be made in the future.
"The actual joint investigation is complete," said Lt. Col Jimmie Cummings, a spokesman for ISAF.
"It is now in legal review and then Gen. John Allen will have to review and make his decision on the findings. He will be looking at recommendations from both U.S. and Afghan investigators."
CNN's Barbara Starr, Chelsea J. Carter and Masoud Popalzai contributed to this report.