BAGHDAD (AFP) - Iraqi police forces said they found a mass grave at the agricultural college in an area that was recaptured from the Islamic State of Iraq and Syria (ISIS) group on Monday (Nov 7).

The grave was found in Hamam al-Alil area, about 14 kilometres from the southern outskirts of Mosul, the last ISIS-held Iraqi city.

"Federal police found a mass grave west of Hamam al-Alil in the agricultural college," the police said in a statement that did not elaborate.

The Joint Operations Command said that "Iraqi forces found... 100 bodies of citizens with their heads cut off" at the college, and that specialised teams would investigate.

Iraqi forces have previously provided estimates of the number of victims in mass graves before they have been excavated and counted.

ISIS overran large areas north and west of Baghdad in 2014, declaring a cross-border "caliphate" that also included territory in Syria.

Its rule has been marked by repeated atrocities including mass beheadings and other executions that it has documented in photos and videos lauding the violence that its supporters share online.

Iraqi forces have since regained much of the territory that ISIS seized, and have uncovered a series of mass graves and massacre sites as they have pushed the jihadists back.

Iraqi forces are now fighting to retake Mosul from ISIS, and Hamam al-Alil was one of the last major obstacles between them and the southern outskirts of the city.