A car bomb has exploded outside a Guardia Civil barracks in the north of Spain after a warning call from Basque separatists, police say.
The explosion at the city of Calahorra, in the Rioja wine region, left one policeman with a minor injury.
Spanish media said the area was cleared before the device went off at 1300GMT.
The Socialist Party of recently re-elected Prime Minister Jose Luis Rodriguez Zapatero said it "forcefully condemns this new attack by Eta".
A man claiming to represent Eta telephoned highway police stating the location, make and colour of the vehicle, at around 1230 GMT, half an hour before the blast, Spanish media reported.
A blue Honda, stolen at gunpoint hours earlier from a couple who were later found trussed up and abandoned in a rural area, was used in the attack, according to Spanish media.
Eta was blamed for the killing of a former town councillor in the Basque region two days before the Spanish general election earlier this month.
The organisation, which ended a 15-month ceasefire in June 2007 after failed peace talks, seeks independence for regions in northern Spain and south-west France.
For more than three decades it has waged a bloody campaign that has led to more than 800 deaths.
Many of those killed have been members of the Guardia Civil, Spain's national police force, and both local and national politicians opposed to Eta's separatist demands.