"There's more about this that we don't know than what we know," said spokesman Lawrence DiRtia. "And what we know is mostly what we're hearing from the Iraqi government."

Iraqi President Jalal Talabani on Wednesday said the bodies of people who had been killed and dumped into the river had been recovered in an area south of Baghdad.

Police said 57 bodies had washed up downriver from a town where unconfirmed reports over the weekend -- later denied by Iraqi officials -- said Shiites were being held by Sunni rebels.

Iraqi police also said Wednesday that the bodies of 19 Iraqi soldiers were found executed in a stadium.

DiRita raised questions about that report as well.

"We don't have any indications that can corroborate the specific numbers involved," he said.

"Apparently there have been some number of individuals discovered in this stadium. The causes of their death, the time of their death, what they were doing and whether they were security forces or not remain in question. There have been reports all across the map on that," he said.

He said the US military had "no independent ability to validate what is coming out of the Iraqi government," which he said was conducting its own investigations.