"Marines, US army soldiers and Iraqi national guardsmen continue joint training exercises in preparation for major assaults against enemy forces in the city of Najaf," the 11th Marine Expeditionary Unit (MEU) said on Wednesday.
US marines, Iraqi national guardsmen, two reinforced US infantry battalions, and a US aviation battalion are "currently working together to constitute the force that will conduct these major assaults," a statement said.
"MEU training with the ING (Iraqi National Guard) began several days ago, and will foster an efficient, effective, cohesive team as ING leads the fight in ridding their city of those who break the rules of law and order," it added.
"Iraqi and US forces are making final preparations as we get ready to finish this fight that the Muqtada militia started," said marine commander in Najaf Colonel Anthony Haslam.
Sporadic fighting continued on Wednesday in the vast cemetery of Najaf, where fighters loyal to Shia leader Muqtada al-Sadr have hunkered down in seven straight days of fighting against US and Iraqi interim government forces.
Medics in Najaf and its twin city of Kufa said 28 people had been killed and more than 110 wounded over the past week.
Al-Sadr aides put the Al-Mahdi Army death toll at 20, while the US military reported four marines killed.
Al-Sadr loyalists say they are
fighting US occupation
Following the US announcement, Arab League Secretary General Amr Musa called for dialogue in Iraq.
"Political dialogue is the only way to put Iraq back on the right track and obtain the departure of foreign troops," his spokesman Husam Zaki quoted him as saying.
"Building a new Iraq requires from all sides the logic of dialogue and not that of military might," Musa said, voicing hope that the Arab League could play a part in "achieving national reconciliation through a national assembly grouping all the sons of Iraq".
Meanwhile, Iran's Supreme Leader Ayat Allah Ali Khamenei has denounced the US military action in Najaf as "one of the darkest crimes of humanity", and said Muslims across the world would respond to it.
"The United States is slaughtering the people of one of the holiest Islamic cities and the Muslim world and the Iraqi nation will not stand by," Khamenei said in an address to cultural attaches broadcast on state television.
"The United States is slaughtering the people of one of the holiest Islamic cities and the Muslim world and the Iraqi nation will not stand by"
Ayat Allah Ali Khamenei,
Iranian supreme leader
"These crimes are a dark blemish which will never be wiped from the face of America. They commit these crimes and shamelessly talk of democracy," he said. "Shame has no place in their vocabulary."
US troops, who have pounded Najaf from helicopter gunships, say they have killed 360 'militiamen'. Al-Sadr's spokesmen say far fewer have died.