A small group of people pick through putrefying human remains laid out on plastic sheets by the side of a road in northern Iraq, searching for any trace of missing friends and relatives.

Some had brought spades to help dig up the mass grave near Suleiman Beg after the town was retaken from Sunni Islamic State militants who held the area until last week.

"They (Islamic State) slaughtered him simply because he was Shiite," said Jomaa Jabratollah, hauling the remnants of his friend, a truck driver, into a coffin, having identified him from the lighter in his breast pocket. "We must take revenge."