Officials said designs included baby bodysuits with the militant group’s emblem and a T-shirt depicting the execution of the British aid worker Alan Henning.
According to a statement from the Spanish interior ministry, a man in Galicia of Spanish nationality has been detained on suspicion of humiliating victims of international terrorism and advocating a terrorist organization.
Investigators told El Mundo that the detainee, who has not been named, spread radical messages in support of “various terrorist groups” on his Facebook profile, in addition to advertising the clothing range.
He was arrested following a joint operation by intelligence agencies and senior police headquarters in eastern Andalusia and Galicia and, the interior ministry said, faces charges of inciting terrorist acts.
The interior ministry said the home and “business premises” of the suspect had been searched and police had seized computer equipment and documents.