Arran, the most prominent radical-left Catalan separatist youth organisation, has claimed responsibility for the vandalism at a Catalan newspaper, Crónica Global, that took place in the early hours of Thursday morning.

The newspaper published video footage and images of the attack, which it said was the fourth such attack in the past few months, and compared it to the street violence and vandalism—"kale borroka"—that took place in the Basque Country during the conflict with Basque terrorist group ETA.

Some windows were smashed with hammers and others painted with graffiti reading "Let...