The fighting began after insurgents fired rocket-propelled grenades at US tanks patrolling Karbala's "Old City," said US Army Col. Pete Mansoor of the 1st Armored Division.

The tanks returned fire, and more than two hours of heavy fighting followed. Smoke billowed from burning buildings. A rebel weapons cache was hit, the military said.

Much of the fighting was near the city's Imam Hussein and Imam Abbas shrines, which US forces allege are being used by militiamen as firing positions or protective cover. Mansoor said the shrines were not damaged. Eighteen insurgents died, he said.

Dr. Abbas Falih al-Hassani of Karbala's al-Hussein hospital said 12 people died, including two Iranian pilgrims. Thirteen were wounded.

The dead included a driver for a camera crew of the Al-Jazeera television network, the station reported.

Rashid Hamid Wali, 40, died while assisting a crew from the Qatar-based network that was filming the clashes from a hotel roof shortly after midnight, said Ahmed al-Sheikh, the network's news editor in Qatar.

It was unclear who was responsible.

There was also overnight fighting between US forces and al-Sadr loyalists in another holy city, Najaf. One civilian died and another was injured when their car was caught in the crossfire, hospital officials said.

AFP adds: Four members of the US-trained Iraqi paramilitary force were killed when they were ambushed by attackers yesterday in the town of Baqubah, north of Baghdad, colleagues of the victims said.

"Four ICDC (Iraqi Civil Defence Corps) were killed and another wounded at 5:30 am local time when they were manning a road block," Abdel Karim Mahmud Hassun said.

"Six cars drove up on two sides and started to fire RPGs (rocket-propelled grenades), grenades and submachine guns," Hassun told AFP.

Separately, a bomb exploded as a US patrol drove past, wounding two Iraqi civilians, five kilometres east of Baqubah.

A US marine serving in the volatile western province of al-Anbar was killed in a road accident while out on patrol, the military said yesterday.

The incident happened Thursday while the 1st Marine Expeditionary Force was conducting "security-and-stability operations," said a statement, classifying the death was "non-hostile".

The latest casualty takes the US military death toll in Iraq to 791 since the start of the US-led invasion in March 2003. This figure includes 576 troops killed in action.