Iraq's government is investigating claims that at least 11 Sunni men have been tortured and killed by police.
Sunni mourners have blamed the police for the recent deaths
Angry mourners at a funeral for some of those killed said they had died at the hands of police and Shia militiamen.
The bodies of the men - one of them reportedly a Sunni cleric - were found in a Baghdad morgue, showing apparent signs of beating and torture.
Earlier this week, nine Sunni Muslim men died after spending hours locked in a police van with little ventilation.
The men, who died of suffocation, had been detained on suspicion of involvement in the insurgency.
Their deaths drew accusations from Sunni politicians and protesters that Iraq's largely Shia police force was brutally targeting the country's Sunni Muslim minority.
An interior ministry official told the AFP news agency he believed the recent killings were the work of men masquerading as security forces.
"There are people who dress up in police or commando uniforms to carry out... horrible attacks which are then blamed on police," Deputy Minister for Intelligence Hussein Ali Kamal was quoted as saying.
He said a committee was investigating this "explosive issue".