Tikrit, Iraq (CNN)Mass graves believed to hold Iraqi soldiers have been discovered in newly liberated Tikrit. Up to 1,700 bodies may be recovered. ISIS claimed to have executed that many soldiers captured in June outside Camp Speicher, a fortified Iraqi base near Tikrit. A total of 47 bodies have been exhumed from two of the 11 mass graves discovered in Tikrit, an Iraqi government official said Tuesday. Hundreds are believed to have been executed by ISIS in June 2014 . Grieving Iraqis, apparently not related to the soldiers, gathered to pray over the bodies. When the first three bodies were found, 10 Iraqi soldiers saluted the dead by firing seven shots into the air. The national anthem was played while soldiers wept. All the bodies were decomposed. Some had their hands bound, Damon said. The remains will be sent back to Baghdad for DNA tests to establish identify, said Ali Tahir, a director in the Iraqi morgue who was supervising the digging and extraction. Damon said there may be eight mass graves inside the presidential palace complex, which contains the residences of former Iraqi President Saddam Hussein, and two other sites outside the city. The presidential palaces complex became ISIS headquarters after the militants occupied the city. Iraqi soldiers and Shiite militias retook Tikrit a few days ago after a fierce battle. Damon interviewed a soldier who said he survived the massacre by playing dead. The solider said ISIS captured the troops outside Camp Speicher and marched them to the presidential palace complex, telling them they would be safe until a prisoner swap was arranged. Once inside the compound, the soldiers were separated into smaller groups, executed and buried in mass graves, the survivor told Damon. He said he was tossed into a river and floated to an embankment. On Monday, Prime Minister Haider al-Abadi said revenge is not the way to deal with the discovery of the bodies. He said several people involved in the killings have been detained. Families of the missing soldiers had been demanding answers from the Iraqi government about what happened. As ISIS swept through northern Iraq in June, some military units were ordered to Camp Speicher. Their families claim the men received orders from their commanders to leave the base and move closer to Baghdad. They left unarmed and in civilian clothes, they say. Military commanders and the Iraqi Defense Ministry denied any such orders being issued and said the men deserted. ISIS released videos that showed what seemed to be an endless line of military recruits marched at gunpoint and later posted images showing cold-blooded mass killings. Damon said Iraqi officials told her it may take weeks or months to exhume all the bodies. Human Rights Watch described the "Speicher Massacre" -- as it has been dubbed in Iraq -- as the "largest reported incident" where "ISIS captured more than 1,000 soldiers fleeing Camp Speicher ... then summarily executed at least 800 of them." Based on satellite imagery and witness testimony, Human Rights Watch last year was able to identity a number of mass grave sites inside Tikrit and the presidential palace complex. The families gave DNA samples to the Iraqi Ministry of Health last year so authorities would be able to match them to unidentified bodies the government may find. CNN's Arwa Damon reported from Tikrit, and Ralph Ellis wrote in Atlanta. CNN's Jomana Karadsheh contributed to this report.
A total of 47 bodies have been exhumed from two mass graves.
Iraqis find mass graves inside presidential palace compound in Tikrit.
ISIS claimed to have executed 1,700 Iraqi soldiers captured outside Camp Speicher.