Kurdish YPG militias, key US allies in the fight against the Islamic State, have burnt entire villages to the ground and terrorised civilians in areas gained from the militant group, Amnesty International has claimed, accusing them of war crimes.

The human rights group has said forces nominally under the control of the autonomous Kurdish administration, led by the Syrian Kurdish political party Partiya Yekîtiya Demokrat, have carried out "alarming" abuses and deliberately displaced thousands they accuse of colluding with the Islamic State. Amnesty International researchers visited 14 towns and villages in al-Hasakeh and al-Raqqa governorates in July and August 2015, documenting the abuses.

One witness told of the YPG threatening to burn residents alive in their homes. "They started pouring fuel in my in-laws' house. My mother-in-law was there refusing to leave and they just poured it around her... They found my father-in-law and began hitting him on his hands... I said, 'Even if you burn my house I will get a tent and pitch it. This is in my place. I will stay in my place,'" she said.

In February 2015 Kurdish forces took control of towns and villages in al-Hasakeh and al-Raqqa, which had been under IS control, and began demolitions, displacing villagers. Lama Fakih, senior crisis advisor at Amnesty International, said the militia were "burning entire villages, displacing their inhabitants with no justifiable military grounds" and that the Kurdish Authority was "abusing its authority and brazenly flouting international humanitarian law, in attacks that amount to war crimes.

"This report uncovers clear evidence of a deliberate, co-ordinated campaign of collective punishment of civilians in villages previously captured by IS, or where a small minority were suspected of supporting the group," she added.

Although the majority of residents affected are Arabs and Turkmen, in some cases, for example in the mixed town of Suluk, Kurdish residents have also been barred by the YPG and Asayish, the autonomous administration's police force, from returning to their homes, Amnesty claimed.