The expulsion of Yazidi families from the Kurdish region of Iraq because a relative joined the Popular Mobilization Forces (Hashd al-Sha'abi) amounts to collective punishment in violation of international law, HRW said.

"These displaced families have the right not to be forcibly returned to their still-damaged home villages," said Lama Fakih, deputy Middle East director at HRW.

The organisation spoke to three Yazidi commanders who said that Yazidi forces had been integrated into the PMF under the name Yazidi Brigades (Kata'ib Ezidkhan), with the forces holding positions in four areas of Sinjar.

Sinjar is technically under Iraqi central government administrative control, but KRG security forces remain active in the area and control the main road from Sinjar to the Kurdistan Region of Iraq.

In late June and early July, Human Rights Watch interviewed nine displaced Yazidis originally from Kocho, Tel Kassab, and Siba Sheikh Khidr villages in Sinjar, which the PMF retook from the Islamic State group in May.

All had been living in the KRI and did not want to return to their villages because of widespread destruction of property, mass graves, unexploded bombs, and the lack of water and electricity.

Their families had fled Sinjar in August 2014, after IS attacked the area, massacring and enslaving thousands of Yazidis.

All those interviewed said that Asayish threatened them with expulsion because they had relatives who joined the Yazidi Brigades, and in four cases, they alleged that Asayish forces had forcibly expelled them to Sinjar as recently as July 5, 2017.

International humanitarian law prohibits collective punishment, which includes any form of punitive sanction or harassment by authorities on targeted groups of people for actions that they did not personally commit.

"While the Kurdistan Regional Government may not like the Popular Mobilization Forces, punishing family members of PMF fighters is the wrong – and unlawful – way to address the issue," Fakih said.

On June 23, Human Rights Watch put the allegations to Dr Dindar Zebari, chairman of the KRG's High Committee to Evaluate and Respond to International Reports - but HRW has not yet received a response.