Another car bomb exploded Wednesday in the Basque region of northern Spain killing a civil guardsman, the local authorities said.

The bomb was planted in a car that exploded at a barracks according to police reports. The blast also wounded four by-passers. The bomb was detonated at about 3 a.m. in Legutiano, Spain, without warning.

The attack wasn’t claimed yet, but authorities are pretty sure that the Basque separatist group ETA is behind it.

"We want to make it clear to the ETA terrorist group that all of the democratic parties are closing ranks to finish off the ETA terrorist group," Socialist Party majority leader Jose Antonio Alonso said in an interview to a Spanish radio.

"I express my condolences to the families of the victims."

This is the sixth bomb attack since the terrorist group ended the one year-old cease-fire in June as peace talks with the government of Prime Minister Jose Luis Rodriguez Zapatero failed. The cease-fire ended in December 2006 with a Madrid airport bombing, CNN reported.

The 41-year-old policeman who was killed was identified as Juan Manuel Pinuel Villalon. He was married and had one child.

About 40 people, including several children, were evacuated from the police building in Legutiano, a town near the Basque region capital city Vitoria.

ETA - Euskadi Ta Askatasuna (Basque for Basque Homeland and Freedom) – is held responsible for more than 800 deaths over the last four decades. As their group name suggests, they fight for an independent Basque country covering parts of what is now northern Spain and southern France.

ETA is part of a faction informally known as the Basque National Liberation Movement. This movement contains several distinct organizations that promote a type of leftist Basque nationalism. Other groups considered to belong to this movement are: the political party Batasuna, the nationalist youth organization Segi, the labor union Langile Abertzaleen Batzordeak (LAB), and Askatasuna among others. There are strong interconnections between these groups as double or even triple membership is common according to the Spanish Authorities.