The Belgian was held under an arrest warrant issued by the Spanish authorities. Spain says the Belgian is currently going under the name Abou Nouh. He is believed to belong to a group of jihadists operating from Melilla, a Spanish enclave in Morocco. He is also said to have ties to the Spanish wing of the terrorist organisation.
The Spanish foreign ministry says that Spanish officers belonging to the country's anti-terrorist unit were involved in the suspect's arrest in the Grand-Duchy.