Spain Interior Minister Alfredo Perez Rubalcaba confirmed that four presumed ETA members arrested on Tuesday morning in Bizkaia''s Bilbao and Galdakao "were part of an ETA cell" with no prior criminal record.

Rubalcaba said that police hoped the arrests would help clear up several unresolved attacks in Vizcaya and surrounding regions but declined to give any details of the detainees'' suspected crimes.

Spanish newspaper El Pais and other media said the detainees were wanted for several attacks including the killing of an anti-terrorism officer in 2009 and the car-bombing of a Civil Guard barracks in the northern city of Burgos the same year.

Rubalcaba described Tuesday''s arrests as being of "enormous importance" and said police had also seized some 200 kilograms of explosives and bomb-making material in the raids.