The pictures, posted over the weekend, purport to show scores of captured Iraqi soldiers being killed by the Islamic State of Iraq and the Levant (ISIL) militant group who wrested control of cities and towns in northern Iraq last week.
The images show masked fighters loading the captives onto trucks before forcing them to lie face-down in a shallow ditch with their arms tied behind their backs. The final pictures show the bodies of the captives soaked in blood after being shot.
A caption on one of the pictures suggested that the victims - believed to be security personnel - were punished for fighting rebels. The Twitter account where the pictures were posted was suspended hours later.
The ISIL and associated forces have taken control of large territories in Iraq in the last week, unging the country into crisis and increasingly splitting communities along lines.
A diplomatic source in Baghdad told Al Jazeera that the pictures were authentic but the number of soldiers executed could not be verified.
Chief military spokesman Lieutenant-General Qassim al-Moussawi also confirmed the photos' authenticity and said he was aware of cases of mass murder of captured Iraqi soldiers in areas held by ISIL.
He told AP that an examination of the images by military experts showed that about 170 soldiers were shot to death.