Dubbed Operation Steel Curtain, the offensive comprises about 3500 troops and includes for the first time units of Iraq's military, numbering about 1000, in what the US insists are joint operations in the al-Anbar province.
US and Iraqi forces say they "have encountered sporadic resistance - mostly small arms fire and improvised explosive devices".
The US military also said only specific targets were selected and there were no reports of military or civilian casualties.
There were fatalities among fighters, the US military added.
At least nine air strikes were called on positions described as "enemy strong points", and a separate strike was carried out against a suspected car bomb, a US military statement said.
Iraqi scouts, described as "specially recruited soldiers from the al-Qaim region," are embedded with the frontline units "and are helping to identify fighter strong points and areas known to contain these homemade bombs".Joint operations
US officials have long blamed foreign fighters saying most of them cross from Syria via the Euphrates valley.
The US forces conducted nine air
strikes on Saturday
The operation involves 1000 Iraqi army soldiers as well as 2500 marines, sailors and soldiers in what the US military called "the largest concentration of Iraqi army forces to take part in an operation in al-Anbar this year".
Steel Curtain follows two earlier operations, Iron Fist and River Gate, also along the Euphrates valley in al-Anbar province.
The US command said there were no reports of casualties among American or Iraqi government forces.
Residents and local leaders say US
bombardment in the Husaiba area were endangering civilians and could lead to greater instability throughout the country.Call for intervention
"We call all humanitarians and those who carry peace to the world to intervene to stop the repeated bloodshed in the western parts of Iraq
," said Shaikh Osama Jadaan, a Sunni tribal leader from the area.
"And we say to the American occupiers to get out of Iraq
and leave Iraq
to the Iraqis."
"...we say to the American occupiers to get out of Iraq and leave Iraq to the Iraqis"
Shaikh Osama Jadaan,
Sunni tribal leader
Husaiba, a poor rural town of about 30,000, is the first stop in a network of communities which the US
military insists has been used by al-Qaida to smuggle fighters, weapons and explosives from Syria
down the Euphrates valley to Baghdad
and other cities.
Many of Husaiba's residents had fled the town after weeks of US military bombardment.
US soldiers killed
One soldier was killed on Friday by small-arms fire south of Baghdad, and another died the same day when the vehicle in his patrol was hit by a mine near Habaniya, 80km west of the capital.
Another soldier was killed on Saturday in a traffic accident in southern Iraq, according to the US military.
Three other soldiers were wounded in the accident.
Those deaths raised to at least 2046 the number of members of the US military who have died since the beginning of the Iraq war in March 2003, according to the Pentagon.
Iraqi soldiers executed
Five Iraqi police commandos were killed on Saturday and three wounded when a roadside bomb exploded in northern Baghdad, hospital officials said.
Al-Qaida in Iraq said on Saturday it executed 15 Iraqi soldiers seized while on leave two days ago west of Baghdad, according to an internet statement which could not be independently verified.
Al-Qaida said it had executed
15 Iraqi soldiers
On Friday, the group warned diplomats in Baghdad to "pack their bags and leave" or face certain death, after claiming a day earlier it had decided to kill two Moroccan embassy employees held hostage for being "loyalists of the oppressors and elements of the apostate regime in Morocco".
In Rabat, the Moroccan foreign ministry scoffed at the idea of closing its Baghdad embassy.
Al-Qaida in Iraq "has nothing to teach Morocco," and Rabat will not succumb to "blackmail," especially "coming from a terrorist group which cannot claim to represent Iraq," the ministry said.
In other violence, 11 members of the same family were killed and three wounded when armed men ambushed their minibus northeast of Baghdad, officials said.
Meanwhile, the White House said that Iraqi Deputy Prime Minister Ahmed Chalabi will meet US Treasury Secretary John Snow and Secretary of State Condoleezza Rice when he travels to Washington later this month - but not with President George Bush.
Chalabi was once a Pentagon favourite who provided volunteers for the embryo of an Iraqi force during the 2003 US-led invasion, as well as erroneous or false information on Saddam's alleged weapons of mass destruction, which were never found.
But he fell out of US favour amidst charges last year that he traded US intelligence to Iran.