MADRID (AFP) - A van exploded outside a civil guard barracks in Spain's northern Basque country on Wednesday, killing one guard and wounding four others, in an attack the government blamed on the separatist group ETA.

Interior Minister Alfredo Perez Rubalcaba said there were 29 people, including five children, inside the barracks which house guards and their families in the village of Legutiano when the bomb went off at 3:00am (0100 GMT).

"They were thinking of carrying out a massacre," he told reporters. "ETA has taken another step with this horrific attack, which is especially evil for its indiscriminate nature and the people and children it could have killed."

The attack used a "significant" amount of explosives and was similar to the bombing of a barracks in the Basque town of Durango by ETA in August 2007 that lightly injured two civil guards, he added.

Prime Minister Jose Luis Rodriguez Zapatero appealed for political unity to defeat ETA, which is blamed for over 820 deaths in shootings and bombings during its four-decade-old fight for an independent Basque nation.

"Together and united, we will bring ETA's end closer," he said in an address to parliament in which he condemned the latest attack as "cowardly, miserable and criminal".

Zapatero was scheduled to travel to Legutiano, located near the Basque capital Vitoria, later on Wednesday to meet with family members of the victims of the attack.

The civil guard killed in the explosion has been identified as Juan Pinuel Villalon, 41. He had been stationed at the barracks for just one month.

The four injured, amongst them two women, were taken to two hospitals in Vitoria where one underwent surgery, Rubalcaba said. Their lives are not in danger.

If the attack is confirmed to be the work of ETA, it will be the sixth death caused by the outfit since it broke a ceasefire in December 2006 with a bombing of a car park at Madrid's international airport that killed two Ecuadoran men.

Before this attack, the last victim of ETA was the former socialist town councillor Isaias Carrasco, who was gunned down in the Basque town of Mondragon on March 7, two days before Spanish parliamentary elections in which Zapatero was re-elected for a second term.

In December, two civil guards were also killed by an ETA team in southwestern France, where they were on an intelligence gathering mission.

ETA announced a "permanent ceasefire" in March 2006 but formally called it off in June 2007 citing frustration with the lack of concessions on the part of the government in their tentative peace process.

The group has since claimed responsibility for about 20 attacks while Spanish authorities have adopted a hard line, arresting dozens of suspected members of the group and Batasuna, its banned political wing.

The people suspected of having triggered the attack fled in a stolen car, which was found by police officers in the nearby town of Abadino.

Rubalcaba said the car had been set to explode but had failed to do so and police were now examining it.

As in other bombings by ETA of civil guard barracks, the group did not phone in a warning ahead of Wednesday's attack as it does when bombing targets used by civilians.

At noon lawmakers observed five minutes of silence in memory of the victims on the steps of Spain's parliament in Madrid while King Juan Carlos and the governor of the Basque region, Juan Jose Ibarretxe, both condemned the attack.

ETA, whose initials stand for Euskadi ta Askatasuna, or Basque Homeland and Freedom in the Basque language, is considered a terrorist organisation by the European Union and the United States.

A French court on Wednesday sentenced former ETA commander Juan Ibon Fernandez Iradi, known as Susper to 15 years in jail.

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