In an effort to purge extremist propaganda from its platform, YouTube has inadvertently removed thousands of videos that could be used to document atrocities in Syria, potentially jeopardizing future war crimes prosecutions, observers and rights advocates say.

“When the conflict in Syria started, independent media broke down and Syrians themselves have taken to YouTube to post news of the conflict,” said Chris Woods, the director of Airwars, a London-based organization that tracks international airstrikes and their effect on civilians. “What’s disappearing in front of our eyes is the history of this terrible war.”

An unspecified number of individual videos and some YouTube channels were deleted in recent weeks after the company put in place new technology to automatically flag and remove content that potentially breached its guidelines. Some videos were reinstated after their creators alerted YouTube.

The company previously relied on its users and a network of trusted monitors to report inappropriate material, which was then prioritized by an algorithm before being subjected to human review.