(CNN) -- A car bomb exploded early Wednesday outside the Civil Guard barracks in the northern Spanish city of Burgos, injuring at least 40 people and causing substantial damage, an Interior Ministry official said.
Officials at Hospital General Yague confirmed that they had received many of the injured, mainly Civil Guard agents and their family members.
Spanish media reported that broken glass and debris caused most of the injuries.
The Interior Ministry official said the attack was likely orchestrated by the Basque separatist group ETA, though neither the Civil Guard nor the police received ETA's trademark warning of a phone call before the attack.
The official said the nature and location of the bombing pointed to the outlawed ETA, which is blamed for more than 800 deaths in its fight for Basque independence.
The last car bombing in Spain occurred on July 9 in the town of Durango, also in northern Spain's Basque country. No one was injured in that attack.