Spanish police have arrested 16 people suspected of praising and encouraging terror acts by three radical Spanish groups.

An Interior Ministry statement on Tuesday said the arrested used Internet social networks to praise past attacks against police and call for fresh ones against politicians, police and others. Other messages were directed against terror victims.

The groups involved included the armed Basque separatist group ETA, Catalonia's Terra Lliure (Free Land) and the shadowy October First Anti-fascist Resistance Group, GRAPO. None has carried out armed actions in recent years.

Ten of the arrests were made in the northern Basque region and the rest in five others.

The main group, ETA, killed 829 people in its Basque independence campaign but declared a permanent cease-fire in 2011. It has not disbanded.