Interior Minister Jorge Fernandez Diaz said the arrests by police early yesterday in the Spanish north African enclave of Ceuta had disbanded and "neutralised" the network.
Fernandez Diaz said those who went to Syria had fought against the regime of Syrian President Bashar Assad and some had taken part in suicide bombings.
He said 12 of the 50 militants who went to Syria had been recruited in Ceuta and the rest in Morocco, adding that some had been minors.
He said that recruits were given training and finance by the network, which had two bases, one in Ceuta and the other in Morocco.
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Once trained to a point where they would be able to carry out terrorist attacks, the recruits were taken to Turkey, where they were transported to the border with Syria before being "introduced to the conflict zones."
The network informed relatives of any deaths, the minister said.
Fernandez Diaz said that when members who had been involved in terror attacks in Syria returned to Europe they remained a threat to security, some as potential "lone wolf" terrorist who needed to be arrested.
He said these types of militants were "highly radicalised and trained" to continue with the jihad or holy war on an individual scale that was "a real and serious threat to our security."