Officials from the CIA have said they believe Saddam Hussein's voice was on the recently released audio tape that warned of more bloodshed in Iraq and urged Iraqis to support resistance to US forces.
CIA spokesman Bill Harlow said the quality of the tape aired last Friday by Arabic TV channel al Jazeera was poor, so that it could not be determined with absolute certainty that it was Saddam Hussein's voice.
The former Iraq leader has not been seen in public since he was ousted from power on 9 April in the US-led war on Iraq.
In a related development, two more American soldiers have been killed in overnight attacks in the Iraqi capital, Baghdad.
A military spokesman said the first soldier died in a firefight with two Iraqi gunmen, one of whom was also killed.
A second man died when an improvised explosive device went off.
In another incident, American troops shot dead two Iraqi civilians during clashes with guerrillas in the town of Ramadi, west of Baghdad.
Witnesses said the troops opened fire on a vehicle carrying the two civilians after an American convoy was ambushed by guerrillas.
Four US soldiers were wounded in the attack.