Two car bombs exploded within hours of each other in two Iraqi cities holy to Shi'ite Muslims.  A blast in the city of Karbala killed at least 12 people and wounded more than 30 others.  Another car bomb exploded in later Najaf, killing at least 45 people and wounding more than 60. 

Both car bombs went off within a few hundred meters of sites holy to Shi'ite Muslims, the shrine of Imam Ali in Najaf, and the Imam Hussein mosque in Karbala.

Hospital officials in Najaf say the death toll there could still rise.  The Associated Press reports that the bomb exploded near a funeral procession for a leading tribal sheikh, and that several of the city's senior government officials were present.

Two hours earlier, in Karbala, a car bomb exploded in the city's main bus station, near a police recruiting center that witnesses believe might have been the original target.  The blast occurred just a few hundred meters from the Imam Hussein shrine, one of the holiest sites in Shi'ite Islam.

Reports from the scene say police cordoned off the area, as firefighters tried to extinguish several burning cars and minibus taxis that caught fire after the main explosion.

It was the second car bombing in Karbala in five days.  An attack near the shrine Wednesday caused similar carnage, and, at the time, some government officials said they thought it was aimed at inflaming tensions between Sunni and Shi'ite Muslims.

A key Sunni Mosque in Baghdad was hit by mortars early Sunday, causing several injuries.  It is not clear who fired them.

Meanwhile, a large group of gunmen ambushed a vehicle carrying election workers in central Baghdad.  Eyewitnesses said the attackers dragged three men from the car and shot them, and then set fire to their vehicle.

The Iraqi electoral commission confirmed that three of its employees had been killed.  The attack happened on Haifa Street, a main thoroughfare that has been the scene of intense clashes between insurgents and American and Iraqi troops in the past.

The electoral commission is responsible for organizing the elections, scheduled for six weeks from now.

U.S. and Iraqi officials have said they expect an upsurge in attacks before the poll, as insurgents try to derail the vote.  But despite questions from some quarters about whether Iraq is stable enough to hold a truly free and fair election, U.S., Iraqi and U.N. officials have said that the poll will be held on schedule.

In another development, insurgents released a videotape of 10 men they claim are kidnapped Iraqi employees of an American security firm.  The men are shown handcuffed and blindfolded, and a voiceover on the tape threatens to kill them, unless their employer stops working in Iraq.