He said units from the US Army 5th Corps were refusing to return fire.

"Coalition forces early Wednesday were receiving fire from Iraqi forces positioning themselves inside the Ali mosque," Ensign David Luckett said here at the US Central Command's forward planning base.

"We're refusing to return fire at the mosque," he added.

The cities of Najaf and Karbala, located further north and closer to Baghdad, are -- after Mecca and Medina in Saudi Arabia -- among the holiest sites in Shia Islam.

Ali, the son-in-law of the Prophet Mohamed and viewed by Shiites as his true successor, is buried in Najaf and the city is a major pilgrimage destination.

A US officer near Najaf said earlier Wednesday that the city, where coalition forces have fought with Iraqi troops for the past three days, was becoming "more and more secure."

SPACE.WIRE