Human Rights Watch (HRW) said the mass grave discovered near Mosul by Iraqi Security Forces 10 days ago contains the bodies of  300 beheaded former local police officers executed by Islamic State.

Joe Stork, Deputy Middle East Director at HRW, said in a statement on Thursday in Cairo that the bodies in the grave appeared to be of men killed in custody.

He cited witnesses as saying they believe that at the end of October, Islamic State massacred several hundred former policemen they had been holding as prisoners.

“Islamic State should be held accountable for these crimes against humanity.

The Iraqi army had earlier said that the same mass grave, discovered on Nov. 7, contained about 100 decapitated bodies thrown into a rubbish pit.

Stork, however, said the grave was found on the grounds of the agricultural college in Hammam al-Alil, 15 kilometres south of Mosul.