At the end of December, more than 3.2 million displaced Iraqis had gone home while 2.6 millions still lived away
The areas were evacuated by Kurdish Peshmerga fighters before the arrival of the Iraqi forces
Iraqi troops and allied forces launched the operation overnight
The only area remaning under control of Islamic State now is a stretch alongside Iraq's western border with Syria
Operation came after IS released what it said was audio recording of its leader Abu Bakr al-Baghdadi urging resistance
Iraqi security forces are in the final stages of the gruelling battle to retake Mosul
The security forces are also conducting a major operation further north in Anbar aimed at retaking the last town
An estimated 400,000 civilians are believed to still be there, unwilling or unable to leave
Local residents said that IS used it as an execution site and a mass grave where they would dispose of victims
More than 20 people have been killed in the bomb blast