Iraq has claimed US Apache helicopters attacked a neighbourhood in the central city of Hillah, killing 33 people and injuring more than 300.
US Central Command is investigating the claims, but says no Apaches could have been involved.
Iraqi officials took reporters to the city 55 miles south of Baghdad and showed them bodies of people killed in what they said was a US attack.
One man said he was on the road from Nasiriyah, heading to Hillah when the attack happened. He said 11 of his relatives were killed when the vehicle they were riding in was hit.
He said the dead included six of his children, his parents and his wife.
Hillah, which lies on the Euphrates River, is believed by the US to be home to a camp for a loyalist militia used to combat internal unrest.
At the Al-Jamhouri hospital in Hillah, journalists accompanied by Iraqi officials saw bodies that included toddlers and a baby of no more than five or six months.
A US Central Command spokesman in Qatar, Lieutenant Commander Charles Owens, said coalition forces had ruled out any possibility that an Apache was involved.
Earlier, Central Command issued a statement saying: "Coalition forces target only legitimate military targets and go to great lengths to minimise civilian casualties and damage to civilian facilities."
Iraqi military spokesmen said that US forces tried a landing on the outskirts of Hillah but were driven away.
AP