A car bomb exploded Friday outside a police station in the Basque city of Durango, slightly injuring two officers, the Basque Interior Ministry said.
A ministry official said the blast appeared to be the work of the separatist group ETA, which called off a cease-fire in June.
ETA called the cease-fire in March 2006, but grew frustrated with a lack of government concessions in ensuing peace talks, and set off a huge bomb in a parking area at Madrid's airport on December 30, killing two people. It insisted then that the truce was still in effect, but finally declared it over in June, and Spanish security forces have been on alert ever since.
ETA has killed more than 800 people since 1968 in its campaign for an independent Basque state.