U.S.-backed Kurdish forces have forcefully displaced thousands of Syrian civilians, mostly Arabs, and demolished villages in northern Syria, often in retaliation for the residents' perceived sympathies for the Islamic State group and other militants, Amnesty International said Tuesday.

Amnesty said its findings were based on visits to 14 towns and villages in the provinces of Hassakeh and Raqqa this summer, areas that are under Kurdish control. It said the abuses amount to war crimes.

The rights group said at least two villages were entirely demolished. In at least eight other villages, the residents were forced to leave, sometimes threatened with being shot or targeted in U.S. airstrikes. It said the victims were mainly Arab, but also included Turkmens and other Kurds.

Amnesty quoted Kurdish fighters as saying the displacement was carried out for security purposes.

A Kurdish official in northern Syria told The Associated Press that forces may have committed minor violations against people suspected of ties to the IS group, but that such actions were not based on ethnicity. The official was not authorized to brief media and so spoke on condition of anonymity.

The Kurds, Syria's largest ethnic minority, have carved out a semi-autonomous enclave in the north since the start of the civil war in 2011.

Kurdish fighters have been among the most successful ground forces battling the IS group. Backed by U.S.-led airstrikes, they defeated the IS group in the Syrian border town of Kobani earlier this year and have since expanded their territory along the border with Turkey.

But Amnesty adviser Lama Fakih said the Kurds' treatment of civilians amounted to collective punishment.

"In its fight against IS, the (Kurdish administration) appears to be trampling all over the rights of civilians who are caught in the middle."

The London-based group called on Kurdish officials to end such abuses, compensate the families for their losses and hold those responsible accountable.

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Associated Press writer Bassem Mroue contributed to this report from Beirut.