Sixteen bodies have been found in a ditch in a town north of Baghdad.
Police said the bodies of adult males found today near Muqdadiya in Diyala province appeared to have been killed recently. Twelve of them had been beheaded, and the other four shot in the head.
Diyala Province, an ethnically and religiously mixed region north of Baghdad, has been the scene of the worst violence in Iraq in recent months.
US forces say al-Qaeda militants have relocated there after being driven out of other parts of Iraq.
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Violence in Iraq has reduced dramatically over the past several months, with the number of attacks countrywide falling by 60 per cent since June, when an additional 30,000 US troops were fully deployed.