At least two mini-bombs have been sent, according to Spain's state-owned EFE news agency. One device exploded at a postal sorting office, slightly injuring the woman who was handling the package.
The group targeted the Roman Catholic archbishop of Pamplona, Francisco Pérez, and the headteacher of a private school belonging to the Legionnaires of Christ movement in Madrid. The archbishop said he vaguely recalled police taking away a suspicious package. "We didn't give it much importance, but later it was said to be a bomb," he said.
The anarchists, who use other names including Artisans Club for New Uses for Coffee, claimed responsibility for the Catholic-targeted explosives in an letter reportedly emailed to an anarchist website. They also claimed to have made a bomb out of an espresso coffee machine packed with gunpowder and shrapnel that was planted at a bank branch.
Police reportedly believe the same group is behind a bomb packed inside a pressure cooker that was left near the public prosecutor's office in Madrid, but failed to explode.
In their letter, the group apparently wrote "Please accept our apologies. Next time we won't fail."