Spanish police arrested the entire leadership of the banned Basque separatist party Batasuna overnight, sparking sharp criticism from Basque nationalists on Friday. The arrests came just days after Spain and Portugal reached an agreement to cooperate in the future investigations regarding the eventual presence of ETA in Portugal.

The Basque separatist party Batasuna is widely regarded as the political wing of the armed separatist group ETA. Local press reported that around twenty-three people were held in the Basque town of Segura, near the coastal city of San Sebastian, as they were about to elect a new leadership for the party.

ETA has had a large part of its infrastructure across the Pyrenees in southern France and has reportedly acquired cars from Portugal, thus raising the possibility that it may have extended its actions there.

In August, ETA members detonated a car bomb on a police barracks in Durango in the Basque region. The explosion led to the injuring of two police officers. They left the scene in a car with Portuguese registration plates. Just two months earlier, terrorists of the same group set a car bomb. The care had been rented in Portugal as well.

Other cases of street violence were reported Tuesday throughout Spain as ETA supporters planted an explosive device at a car dealer in the Basque capital Vitoria and attacked a bank teller with petrol bombs in Arbizu, near Navarre region.

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.