Four explosions have occurred near a power station half-owned by the ESB in Spain's northern Basque region.
An ESB spokesman has confirmed that the Amorebieta plant has been evacuated and a full security operation is underway.
The power station, which is in the final stages of commission, is manned mostly by a local Spanish workforce.
No injuries have been reported, and there was no immediate word of any damage to the power station.
The blasts were claimed by the Basque separatist group, ETA, which last summer staged a series of bombings on electricity lines in an apparent attempt to disrupt Spain's infrastructure.