"The decapitated man and the woman, who was shot dead, were brought to the hospital last night" by the Iraqi national guard, according to a hospital official in the town of Mahmudiya, 40km south of Baghdad.
He said they had no identity papers on them and their nationality could not be determined.
The hospital said the woman had been found wearing jewellery, indicating it was not a case of common crime.
An Iraqi national guard spokesman had said earlier that the two victims were Iraqis and their bodies were found on Saturday night on the road near Yusifiya, 20km south of Baghdad.
The area around Yusifiya and the neighbouring towns of Mahmudiya and Latifiya are known to Baghdad residents as the "triangle of death".
The area sees almost daily attacks on US military convoys, Iraqi security forces, truckers suspected of transporting goods for US forces, and foreigners travelling the main north-south roads which traverse the area.