In what appears to be the first Basque separatist attack following weekend elections, a bomb exploded Monday, killing a policeman.
Suspicion fell on the separatist group ETA, which has operated in this region of northern Spain since 1968.
A police spokeswoman said the officer, 36-year-old Ramon Doral, died an hour after the bomb went off.
Initial investigations indicate the bomb was placed underneath a car, but it was not immediately known if the vehicle belonged to Doral.
Although no group has admitted responsibility for the blast, the police spokeswoman, who spoke anonymously, said it appears to be the work of ETA.