Witnesses say explosions and machine-gun fire echoed in the heart of Al-Najaf as U.S. helicopters flew overhead. Smoke also could be seen rising from several places near the city's ancient cemetery, which has been the scene of close-quarter fighting in recent days.
The fighting rages despite a visit to the city on 8 August by Iraq's interim Prime Minister Iyad Allawi aimed at calming the situation. Allawi called on Imam Al-Mahdi Army fighters loyal to radical Shi'a cleric Muqtada al-Sadr to stay away from Al-Najaf's holy sites.
"Unfortunately, there are people who have done things against the law who are trying to hurt this city -- this heroic and steadfast city. We came here to check the city and to hold talks with the governor, whose position is a heroic one and an honorable one. We also came here to talk with the police and members of the National Guard. And we hope that this matter will end as soon as possible. We believe the gunmen should leave the holy sites quickly, lay down their weapons
and return to the rule of order and law," Allawi said.
Al-Sadr vowed on 9 August to fight what he called the "occupation of Al-Najaf" until the "last drop of blood" is spilled.
Those remarks prompted a warning from Iraqi Defense Minister Hazim Sha'lan al-Khuza'i. Speaking to Dubai-based Al-Arabiyah television, Sha'lan al-Khuza'i said the Iraqi Army "will surely intervene" and join the U.S.-backed
military operations in Al-Najaf if the crisis continues to grow.
Sha'lan al-Khuza'i also claimed al-Sadr's militia is receiving weapons from Iran. And he said Shi'a fighters from the southern Iraqi cities of Al-Basrah, Al-Nasiriyah, Al-Diwaniyah and Hilla have moved to Al-Najaf to support al-Sadr's fighters.
The U.S. military estimates it has killed some 300 insurgents in Al-Najaf since 5 August. Iraqi officials and militia leaders put the death toll much lower.
Lieutenant Colonel John Lewis Mayer is the commanding officer of U.S. ground combat operations in the area. Mayer has accused al-Sadr's fighters of launching more than 100 mortar rounds at U.S. forces from within the compound of the city's Imam Ali Mosque.
Mayer says his troops also have engaged in hand-to-hand combat with militia fighters in the city's sprawling cemetery. He says militia fighters have been using crypts there for arms storage and have been smuggling weapons into the area inside coffins.
"We did not pick this fight. We were down there assisting our partners who are the Iraqi police and the Iraqi National Guard, and, of course, the governor of Najaf. We were asked to assist on behalf of the governor of Najaf, and [the U.S. Marines'] motto is, 'No better friend, no worse enemy.' The Iraqi police have been our friends since the liberation. When they're attacked, it is like attacking a United States Marine. And so we went down there to assist in a battle we did not ask for, but [a battle] we were not going to run away from either," Mayer said.
The violence follows an uprising by Shi'a militants across southern and central Iraq in April and May and a later cease-fire.
For more on the situation in Iraq go to RFE/RL's special page, "The New Iraq."