The US military accused the international media on Saturday of exacerbating Iraq's violent tensions by reporting false claims of massacres which it said were deliberately fabricated by extremist groups.
This week several newspapers and agencies reported that Iraqi police had found 20 beheaded corpses in Salman Pak, south of Baghdad.
AFP did not carry the report after its sources were unable to confirm the rumour.
"It now appears that the story was completely false and fabricated by unknown sources," a statement from the US military said.
"Anti-Iraqi forces are known for purposely providing false information to the media to incite violence and revenge killings, and they may well have been the source of this misinformation," the statement alleged.
Central Iraq is in the grip of a brutal war between rival political and sectarian forces, and insurgent death squads often murder civilians. It is often hard to find independent information on specific incidents.
"Extremists promote falsehoods of mass killings, collateral damage and other violence specifically to turn Iraqis against other Iraqis," Rear Admiral Mark Fox, chief spokesman for the US-led coalition in Iraq, said.
"Unfortunately, lies are much easier to state, the truth often takes time to prove," he added, in the statement which urged the media to give US and Iraqi officials time to check out reports of violence.