An explosive device went off early Tuesday outside a police station in the Basque region, Basque police said. No injuries were reported.
The device caused damage in a garage and inside the police compound and shattered windows in nearby houses in the town of Zarautz in the Vizcaya province, the capital of which is Bilbao, police said in a statement.
There was no warning of the attack but the Basque Interior Ministry suspects of the armed Basque separatist group ETA for the explosion, news reports said.
On Sept. 10 police defused a car bomb outside a government building in northern Spain after its detonator malfunctioned.
Earlier this month, the armed group, which called off a cease-fire in June and resumed full-scale attacks in late August, warned in a statement it would continue to hit targets of the Spanish state.
ETA, whose name stands for Basque Homeland and Freedom, has waged a violent, explosion-filled campaign for an independent Basque state since the late 1960s. More than 800 people have been killed by ETA attacks.