MADRID (AP) — Spanish police say they have arrested nine activists linked to pro-Catalan independence groups they suspect may have been preparing to commit violent acts, possibly with explosives.

A Civil Guard statement said the operation Monday was part of an investigation into the Committees for the Defense of the Republic, a grass-roots organization that favors northeastern Catalonia's independence from Spain and in the past has organized street protests and blocked road and rail transport.

Police said they carried out 10 raids and seized an abundance of material and substances they believe could be used to make explosives.

Protests in Catalonia are expected in the coming weeks when Spain's Supreme Court issues its verdict in the trial of 12 ex-officials and activists charged for attempting to establish an independent Catalan republic in 2017.