Police in the Iraqi city of Najaf say at least three civilians have been killed in a car bombing Saturday, less than a week after an attack there killed 52 people.

Initial details are sketchy, but police say the incident occurred on the highway between the Shi'ite holy cities of Najaf and Karbala and appeared to have targeted a U.S. military convoy. There was no word on whether there were U.S. casualties.

Meanwhile, Najaf's governor says police have arrested a group of men suspected of having organized last Sunday's attack and an announcement would be made in Baghdad next week.

In Baghdad, it was a bleak Christmas for the city's small Christian community. Further unnerved by an apparent suicide attack Christmas Eve that killed nine people, the city's churches were mostly empty today.

Some information for this report provided by AFP, AP and Reuters.