"We have received 500 corpses and 375 others injured people," said Dr. Kifah Muhammad, the manager of the hospital in Sinjar, a town in western Nineveh province.
He added that the death toll could rise further as rescue workers continue to ferry the victims to the hospital.
The newly obtained figure from the hospital doubled the death toll Xinhua earlier got from a local police source, which said that 250 people were killed and 300 others injured.
Late Tuesday, four suicide car bombs, apparently targeting residents from Iraq's Yazidi religious minority, ripped through Yazidi residential compounds in Kahtaniya and al-Jazeera near Sinjar.
The Yazidis are primarily ethnic Kurd and mostly live near Mosul,capital of Nineveh province.
The coordinated attack on Tuesday recorded the deadliest incidents of its kind since the Iraq war broke out in 2003.
The last bloodiest attack took place on Nov. 23 of 2006, when a series of bombings and mortar rounds killed more than 200 people and injured more than 250 others in Baghdad's Shiite neighborhood of Sadr City.
However, the U.S. military gave a lower death toll in a statement on Wednesday despite the lurid death toll from hospital.
The military said in the statement that some 60 Iraqi civilians were killed and an unknown number injured in the five car bombs in western Nineveh province, one more bomb than what the media reported.
Four car bombs struck Kahtaniya near the Sinjar region while another car bomb detonated in a residential area of al-Jazeera, southwest of Khahtaniya, it said.
So far, no any group has claimed responsibility for the attack. However, many people blamed it on al-Qaida terrorists in Iraq, who were forced to leave Anbar and Diyala provinces amid a joint massive U.S.-Iraqi offensive against them and commenced staging attacks in other vulnerable areas, such as Sinjar.