US and Iraqi forces are conducting a massive search for three soldiers missing since their patrol was attacked south of Baghdad on Saturday.
US and Iraqi troops searched the farms near Mahmudiya
Five soldiers were killed in the insurgent attack on the patrol of seven Americans and their Iraqi interpreter near the town of Mahmudiya.
Roadblocks have been set up to prevent the soldiers being moved from the area.
A US military spokesman said the search would continue until the fate of the missing soldiers was known.
The area around Mahmudiya has been the scene of frequent attacks by insurgents against US troops.
The patrol was attacked 11km (seven miles) west of the town at 0444 (0044 GMT), spokesman Maj Gen William Caldwell said.
On Sunday, a group associated with al-Qaeda in Iraq, calling itself Islamic State in Iraq, posted a statement on the internet claiming responsibility for the attack and saying that it was holding the missing soldiers.
The group offered no proof to back up its claim.
A nearby unit heard the attack but could not establish contact with the patrol, Gen Caldwell said.
An unmanned aerial surveillance drone then spotted two burning vehicles 15 minutes later.
A rapid reaction force was sent and a huge operation was launched involving helicopters, unmanned aerial vehicles and fixed-wing aircraft, to try to find the missing men.
The US military said it was talking to local leaders to try to enlist their help in the search.
Checkpoints have been set up on roads leading away from the area and west into Anbar to prevent the soldiers being taken to an insurgent base.
US and Iraqi troops combed farms and orchards in the area of the attack and the search continued overnight with the use of thermal imaging equipment.
"Make no mistake: we will never stop looking for our soldiers until their status is definitively determined, and we continue to pray for their safe return," said Gen Caldwell.
The US military has not clarified if the Iraqi interpreter was among the missing or those killed.
In the past year, six US soldiers have been abducted and killed by insurgents in two similar incidents.
The bodies of two soldiers were found days after they went missing in the same area last June, while four soldiers were abducted and killed by insurgents in Karbala in January this year.
An extra 30,000 US troops are being deployed in Baghdad and Anbar province as part of a four-month old joint Iraqi-American security drive.
US commanders say the "surge" in troops has reduced the number of sectarian murders in the capital but the number of car bombings remains undiminished at more than 100 a month, says the BBC's Andrew North in Baghdad.
More than 3,300 US soldiers have been killed in Iraq since the war began in March 2003.