Madrid/Vitoria, Spain  - A car bomb blast killed a police officer and injured four others at a barracks of Spain's paramilitary Civil Guard in the northern Basque region early Wednesday, Interior Minister Alfredo Perez Rubalcaba confirmed.

The minister attributed the attack to the militant Basque separatist group ETA, vowing that it would not "scare" the government which was determined to track the killers down.

A van containing more than 100 kilogrammes of explosives was parked at the entry to the barracks in Legutiano 15 kilometres north of the regional capital Vitoria, according to police sources.

The explosion caused the roof of the building to collapse, killing Juan Manuel Pinuel Villalon, 41, married with one child.

Two male and two female officers were injured. The most seriously injured victim was rescued after being buried in rubble, but hospital sources said his life was not in danger.

Pinuel was hit just as he was making a phone call to inform a security centre about the presence of a suspicious van, according to police sources.

Nearly 30 people, including five children, were inside the barracks when the bomb exploded, Rubalcaba said, accusing ETA of wanting to cause a "massacre."

The blast tore a several-metre-wide crater in the ground, destroying the van completely and shattering windows of nearby buildings. The explosion was heard as far as three kilometres away.

The attackers did not give an advance warning, as ETA often does, an indication that they intended to kill.

Police located an abandoned car which the attackers apparently used to flee, defusing an explosive device which had been planted inside to destroy evidence.

The parliamentary parties approved a joint declaration, vowing to "respond with unity and firmness" to ETA until it would be "definitively defeated."

Basque regional Justice Minister Joseba Azkarraga said an attack had been expected, because ETA continued to have the capacity to kill and it had announced combat "on all fronts."

Pinuel was ETA's sixth suspected victim since Socialist Prime Minister Jose Luis Rodriguez Zapatero's attempt at a peace process collapsed with a car bombing at Madrid airport in December 2006.

The government has adopted a tough line against ETA since then, arresting dozens of its suspected members or collaborators.

The most recent victim before Pinuel, former Socialist councillor Isaias Carrasco, was shot dead two days before the March 9 elections, after which Zapatero formed a new government. ETA has also staged smaller attacks which usually caused no injuries.

ETA has killed about 830 people in its 40-year armed campaign for an independent Basque country carved out of northern Spain and southern France. (dpa)