Scottish soldiers from the Black Watch regiment and a force from the US 24th Marine Expeditionary Unit (MEU) cordoned off several kilometres of the west bank of the Euphrates river on Wednesday, 50km south of Baghdad.
They said they were scouring villas and farms for anti-US fighters and hidden stocks of weapons.
US and Iraqi troops rounded up 15 suspected anti-US fighters during the operation, the military said in a statement, raising to 210 the number detained in the past eight days of raids.
It was the latest in a series of aggressive raids across the region since the launch a week ago of what American commanders have called Operation Plymouth Rock.
In a separate incident, the army said an Iraqi fighter attempting to plant a roadside bomb along a highway through the area was killed when one of the two mortar rounds exploded prematurely.
Fierce clashes have erupted since
the US-led offensive started
Following on from their assault last month on the city of Falluja, 60km upstream, the latest operations are part of an effort to stifle anti-US activity before a national election planned for the end of January.
Some Iraqi groups say the elections will be illegitimate because Iraq is still an occupied country. They argue the elections will exacerbate divisions between different Iraqi communities.
In other developments, three Iraqi children were killed and five others, all from the same family, were injured when a rocket-propelled grenade was fired at a house in al-Yarmuk neighbourhood in Baquba, west of Baghdad, medical sources told Aljazeera.
In Hibhib, northeast of Baquba, a senior leader of the Islamic Dawa party, Abd al-Amir Hasan, was killed when armed men opened fire on him.
And in Falluja, clashes erupted on Tuesday evening in several neighbourhoods between US forces and Iraqi fighters in the Julan neighbourhood.
"The forces locked the house's external gate and treated all the people inside, including the Red Crescent employees, very badly. There was an atmosphere of extreme rage among the citizens"
Abu Ayub al-Isawi, a witness to Falluja clashes
Abu Ayub al-Isawi, a witness to the fighting, told Aljazeera that US forces called on Falluja families through loudspeakers to head towards the Red Crescent centre in a house in al-Shurta neighbourhood.
"US forces then surrounded the Red Crescent centre after people had arrived there to receive aid supplies, preventing anyone from exiting it," he said.
"The forces locked the house's external gate and treated all the people inside, including the Red Crescent employees, very badly. There was an atmosphere of extreme rage among the citizens."
He added: "US forces later allowed only women, children and males, aged under 15 and above 55, to get out."
Moreover, unrest continued in many areas of Iraq on Wednesday.
In the northern city of Kirkuk, three Iraqis were injured when an explosive device targeting a US military convoy detonated in Bajwan district.
In Mosul, clashes erupted between US forces and Iraqi fighters in the industrial area west of Mosul city. Casualties among the two sides are not yet known.
And in Latifiya, south of Baghdad, a number of US soldiers and Iraqi national guards were injured when a car bomb exploded at a joint checkpoint on a bridge.
A US Humvee was also destroyed in the attack.
Talib al-Janabi, an Iraqi journalist, told Aljazeera that "casualties are unknown as yet as US forces have closed all roads leading to the explosion site".