Two hands are seen poking from the ground as Iraqi forensic teams recover dead bodies from a mass grave in the presidential compound of former Iraqi president Saddam Hussein in Tikrit on Monday. Photo: AFP

Iraqi forensic teams began on Monday excavating 12 suspected mass grave sites thought to hold the corpses of as many as 1,700 soldiers massacred last summer by Islamic State (IS) militants as they swept across northern Iraq.

The mass killings in June of Shiite soldiers from Camp Speicher, a former US base outside the Sunni city of Tikrit, has become a symbol of the brutality of IS fighters and their hatred for Iraq's Shiite majority.

The deaths showed Iraqis that the IS fighters, who have also attacked ethnic and religious minorities as well as fellow Sunni Muslims opposing them, were a threatening new kind of foe.

The images of Shiite soldiers being machine-gunned in their hundreds, posted online by the jihadists, could rank as the deadliest single act of bloodshed during a decade of periodic sectarian war in Iraq.

The exhumation of burial sites on the late dictator Saddam Hussein's Tikrit presidential compound came days after IS militants were driven from the city by Iraqi forces and Shiite paramilitaries.

"We dug up the first mass grave site today. Until now we found at least 20 bodies. Initial indications show indisputably that they were from the Speicher victims," said Khalid al-Atbi, an Iraqi health official working with the forensic team sent to Tikrit.

"It was a heartbreaking scene. We couldn't prevent ourselves from breaking down in tears. What savage barbarian could kill 1,700 persons in cold blood?" he asked.

Survivors of Speicher have described to Reuters their ordeal in June as the Iraqi military chain of command unraveled and Sunni IS fighters descended on Tikrit, rounding up Shiite soldiers for slaughter.

The victims' families, who often grow angry at Iraq's political class for failing to provide them proper answers, have wondered for months about the fate of their friends and loved ones.

"The only positive thing is the victory in Tikrit," said, Ali Hamad, whose cousin Kamal went missing at Speicher.

"We are happy. At least the families will soon know the fate of their sons and cousins," he said.