( CNN ) -- An explosion killed at least 21 militants in Iraq Monday , apparently when a lesson on car bombing went wrong , police said . Police said they found a camera inside a house where the blast took place , leading them to believe someone was filming the installation of explosives into a vehicle for propaganda purposes . After a loud explosion , security officials rushed to the scene and found body parts , mostly of young men , scattered about . Six people were critically injured . Security forces arrested four men fleeing . Police said they believe the house was a small training base for the al Qaeda-affiliated Islamic State of Iraq and Syria ( ISIS ) . They also found documents and flags usually used by al Qaeda-linked groups such as ISIS . The explosion happened inside a remote house northeast of Samarra , a predominantly Sunni town about 110 kilometers ( about 68 miles ) north of Baghdad . Separately , shootings and explosions across the country killed at least 14 people and wounded 29 others , police officials in Baghdad , Mosul and Ramadi told CNN .
Authorities found a camera inside the house . 6 people were critically wounded in the blast ; 4 others were arrested . Police think the house was a training base for al Qaeda-linked group .