A small, homemade explosive device detonated Saturday night outside a bicycle factory in the capital of Spain's Basque region, causing no injuries and only minor damage, Basque police said.
They said there was no claim of responsibility and police were investigating at the scene of the blast in the city of Vitoria. The factory was empty at the time of the explosion, police said.
It appeared similar to other blasts blamed on or claimed by the armed Basque separatist group ETA in recent weeks and months.
ETA has killed more than 800 people since the late 1960s but has not staged a fatal attack since May 2003.