 The Sunni Muslim attack on the Shiite mosque took place on Ashura, the day on which Shia Muslims commemorate one of their first Imams. It's a day that's a frequent source of tension between the two Muslim sects. Four of the victims of Monday's attack were from Pakistan and one was from India. A policeman also died in the shootout. The violence has raised fears that the normally safe Gulf states may now be a target for a newly resurgent Islamic state.