Amnesty International accused a Syrian Kurdish militia supported by the United States of committing war crimes by driving out thousands of non-Kurdish civilians and demolishing their homes.
The watchdog group documented cases in more than a dozen villages in Kurdish-controlled areas where YPG, or People's Protection Units, forced residents to flee or destroyed their homes.
The Kurdish militias have seized swathes of northern Syria from Islamic State militants this year.
Amnesty's senior crisis adviser, Lama Fakih, said on October 13 that the autonomous Kurdish administration was "flouting international humanitarian law, in attacks that amount to war crimes."
YPG spokesman Redur Xelil called that a "false allegation."
But Amnesty quoted Kurdish militiamen admitting to forced displacements, which they said were "isolated incidents" where civilians were moved for their own safety.
The YPG has been the most effective partner on the ground for a U.S.-led air campaign against IS. It has previously denied Turkish accusations of deliberately driving out Arab and Turkmen civilians from areas under its control.