The grave was discovered on Friday in Buhrez distric of Diyala Province, 65 km northeast of Baghdad based on information from a resident in the area.
“The skeletal remains appear to have been in the grave for a long time,” an official from the Iraqi Human Rights Ministry was quoted by Xinhua as saying.
The responsibility for the killing and burial of the mass grave is not yet officially clarified, as the site is still under investigation.
Such investigations began after US-led forces invaded Iraq in 2003. The majority of the found bodies are reported to be Shia and Kurd.
The US-led invasion in 2003 was based on allegations that Iraq harbored weapons of mass destruction (WMD). Later findings, however, proved that the country was not in possession of the arms, and that the US officials who rallied support for the invasion knew about this.
Iraqi civilians regularly got caught in the crossfire between the militants and the troops during and after the invasion.
Analysts believe the recent wave of violence which has hit Iraq is a plot devised in Washington to create a sense of false insecurity to provide a pretext for the extension of US military stay in the oil-rich country beyond the December 2011 deadline.
The California-based investigative organization Project Censored says over one million Iraqis have died during the US military presence.