A bomb exploded Wednesday outside the offices of a political party in the northern town of Santona, no one was injured, according to Spanish news reports.
The device detonated at 8 a.m. (0700GMT) outside the offices of the right-wing Falange political party, Spanish national radio RNE said.
Police cordoned off the area around the offices before the device exploded after receiving a telephone warning from someone claiming to be part of the Basque separatist group ETA, RNE said.
Spanish news agency Efe said police found a bag with a sign saying "Danger bomb" outside the Falange offices.
There were significant amounts of broken glass around the area after the explosion, RNE reported.
ETA is blamed for more than 800 deaths since the late 1960s in its struggle to create an independent Basque homeland, although its last fatal attack occurred in May 2003 when a car bombing killed two policemen.
Prime Minister Jose Luis Rodriguez Zapatero offered to negotiate with ETA in May 2005 if it renounced violence, but the militant group has kept up a campaign of low-level violence, setting off dozens of explosions, reports the AP.
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