Nine bodies and 10 severed heads have been discovered near Miqdadiya, north-east of Baghdad, Iraqi police say.
Such gruesome discoveries have become rarer since 2006
The 19 victims were all male and some had died in recent days, said a Diyala province police spokesman.
The nine intact bodies were handcuffed and had been shot dead, local medical sources said.
Diyala province is where US and Iraqi forces have been carrying out major operations against Sunni militants.
Such gruesome discoveries were almost commonplace about 18 months ago when central Iraq was caught in a frenzy of sectarian killing between Shia Muslims and their Sunni Arab counterparts.
However, security improved during 2007 as the US military boosted troop numbers and many in Iraqi society rejected the descent into violent sectarianism.
Separately on Tuesday, two people were killed and about 20 were wounded in a series of bomb blasts in Baghdad.
In the northern city of Mosul, where five US soldiers were killed on Monday, a suicide bomber targeting a US patrol injured 10 Iraqis.