A source from the Iraq Interior Ministry said the corpses were found blindfolded, with their hands tied behind their backs.
He said some of the victims had been beheaded or repeatedly stabbed.
Many bodies showing signs of abuse have been found in Iraq in recent months.
Elsewhere in eastern Baghdad a US helicopter fired rockets into a crowded Shia neighbourhood killing at least one Iraqi woman.
US military officials said the attack was in retaliation after the aircraft came under fire from the ground.
The military also reported five new military deaths in a series of attacks across Iraq.
On Wednesday a roadside bomb killed three US soldiers south of Baghdad, while a fourth died the same day from wounds sustained in a small-arms fire attack in the capital's southwest.
Also on Wednesday a US marine was fatally wounded during combat near the western city of Falluja.
The fatalities bring the number of US military deaths to 2247 since the invasion of Iraq in March 2003.