A bomb exploded in northern Spain early morning, shortly after officials said they received a phone call from warning of the blast.
The explosion happened in the town of Santona outside the offices of the right-wing Falange political party. Local authorities say someone claiming to be a part of the Basque separatist group E.T.A. called minutes earlier.
Officials say the building sustained significant damage, but no injuries have been reported.
E.T.A. has been blamed for more than 800 deaths during a four-decade-old campaign for an independent Basque homeland. In recent years, it has carried out a campaign of low-level attacks that have caused no serious injuries.
Some information for this report was provided by AP and Reuters.