The operation began one year ago as an investigation into a child pornography network by Spain's National Police force.
Investigators discovered the network's members discussing online sexual abuses they allegedly committed and plans to kidnap children to imprison and use in orgies, TheLocal.es reported Monday.
Authorities said at least three children in Spain were in immediate danger.
A raid led to the arrest of eight suspects between the ages of 25 and 50 in La Coruna, Pontevedra, Madrid, Gijon and Malaga, the news website said. Four of them were immediately imprisoned.
Those detained were charged with intention to commit murder, sexual assault, molestation, corruption of minors, human trafficking and possession of child pornography.