Up to this point , Spain 's deadliest terrorist attack had been the El Descanso bombing in Madrid by suspected Islamic militants which had killed 18 Spaniards and injured 82 others , including 11 American servicemen , who were believed to be the target of the attack . The ETA attack which had caused the most fatalities had occurred on 14 July 1986 when a car bomb on República Dominicana Square in Madrid had killed 12 civil guards and injured 50 people
car bomb on República Dominicana Square
Plaza República Dominicana bombing
Hipercor bombing