America's top soldier has contradicted officers on the ground in Iraq by denying a Saddam-era general has been given control of the city of Falluja.
Shia militants have killed at least two US soldiers this weekend
Gen Richard Myers, chairman of the US Joint Chiefs of Staff, said he did not believe Gen Jasim Saleh would pass the vetting process for taking command.
Gen Saleh has been in the city with 200 Iraqi peacekeepers since Friday.
Nine US soldiers died in attacks on Sunday, taking to 12 the death toll for the first two days of May.
April saw the highest US combat losses in Iraq since the invasion last March, with 129 killed.
In the bloodiest attack on Sunday, two mortars hit an unidentified base in western Iraq, killing six soldiers
'Blood all over'
US marines would only say that the base was located two hours' drive west of Falluja, itself 50km (32 miles) west of the capital Baghdad.
"I didn't know who was dead and who was wounded," an unnamed 27-year-old survivor was quoted as saying by Reuters news agency.
"I knew it was a mortar from the black smoke... It was a bad day."
The witness said two bombs had fallen, the second directly on soldiers seeking shelter after the first blast.
A survivor quoted by AFP news agency described a scene of chaos:
"When it hit, everybody went down, took cover, there were people screaming. It knocked me off me feet... I saw blood all over, I didn't know whose it was, mine or other people's."
In other violent incidents:
- A bomb and gun attack on a US base near the northern oil city of Kirkuk leaves one soldier dead and 10 injured.
- Militants kill two US soldiers and two from the Iraqi Civil Defence Corps in an early-morning attack in north-west Baghdad.
The US reports the deaths of two soldiers near Amara on Saturday, ambushed by Shia militants.
Gen Saleh led his men into Falluja on Friday night after US forces pulled back following weeks of bloody fighting in and around the Sunni city of 300,000.
But Gen Myers told Fox News that Gen Saleh had not been put in charge.
The former general under Saddam Hussein and another unnamed Iraqi general were still being considered for the position, he said.
Bodies are still being found in the ruins of Falluja
"My guess is, it will not be Gen Saleh... he will not be their leader," Gen Myers said.
The US commander denied that this amounted to a change in policy and blamed "reporting" of the issue, saying it had been "very, very bad and way ahead of the facts".
Gen Saleh has denied ever serving in Saddam Hussein's feared Republican Guard and says he accepted his task in Falluja only to prevent further bloodshed.
Doctors there say at least 600 people were killed and thousands fled during the siege which began on 5 April.
As masked gunmen in Falluja celebrated the US withdrawal, marine officers warned they would give Gen Saleh only a few days to disarm them.
Lt James Conway, commander of the 1st Marines Expeditionary Force, said on Saturday that Gen Saleh would be "expected to provide security" and the marines planned to send a convoy through the centre of Falluja "in a very few days".