MADRID -- The Interior Ministry says four people have been arrested in northwest Spain on suspicion of belonging to a violent, regional pro-independence group.

The ministry said in a statement that two of the arrests were made in the port city of Vigo on Saturday after police discovered two primed explosive devices in the trunk of a car, and two other suspects were arrested early Sunday.

It said the "suspected terrorists" belong to "the Galician Resistance" -- a group of which little was known until November 2011 when another member was arrested in possession of explosives.

Spain has nationalist groups in Galicia, Catalonia and the Basque region, where armed group ETA has killed more than 825 people in a four-decade campaign to carve an independent state in northeastern Spain and southwestern France.