BAGHDAD (Reuters) - The Kurdish Asayish police force in Iraq last year executed dozens of Islamic State fighters in their custody and disposed of their bodies in a mass grave northwest of Mosul, Human Rights Watch said in report on Friday.

A Kurdistan Regional Government (KRG) security official did not return Reuters calls to comment. HRW’s report cites a KRG official, Dindar Zebari, who denied executions took place.

He said the bodies belonged to militants who were killed fighting and “were probably brought in one place to be buried.”

“Because the mass grave site is located within the flood zone of the Mosul Dam reservoir, it is critically important to urgently allow international forensic experts to conduct a detailed exhumation of the site before seasonal rains fill the reservoir again later this year,” the HRW report said.

The KRG’s Peshmerga fighters in July assisted a U.S.-backed offensive by Iraqi forces to capture Mosul, the de facto capital of the Islamic State “caliphate” declared in 2014 over parts of Iraq and Syria.

Iraq declared victory over Islamic State in December but the group has morphed into an underground organization and continues to claim attacks across Iraq.

Link to the HRW report: bit.ly/2BQzKU0