The Basque separatist group Eta has been blamed for four explosions near a power station in northern Spain on Tuesday. There were no casualties.
Spanish officials said the blasts, in the town of Amorebieta, came shortly after warnings in the name of Eta.
Workers at the power plant were evacuated before the explosions. Witnesses were quoted as saying the blasts were small.
Eta has been waging a violent campaign since 1968 to win Basque independence.
The Amorebieta plant was undamaged by the explosions, Basque officials said.
The blasts came about 30 minutes after warning calls were made to the Basque newspaper Gara and to Basque emergency road services.