Spanish police arrested on Monday nine people linked to Catalonia's pro-independence movement who prosecutors said were plotting violent acts in the coming weeks and had been charged with terrorism and possessing explosives.

Two were later released, said acting Interior Minister Fernando Grande-Marlaska.

Hundreds of pro-independence protesters rallied late on Monday in Barcelona and Sabadell, demanding that those detained be freed and that Madrid "end repressions" in the region.

The Spanish High Court's prosecutors said in a statement the court had ordered the arrests to prevent the unspecified actions which "could have caused irreparable damage due to the advanced stage of preparations."

They said the court was certain the actions were planned for some time between the anniversary of Catalonia's October 1, 2017, independence referendum and the announcement of the verdict in a trial of separatist leaders in Madrid – widely expected in the first half of October.

The head of Catalonia's government hit back, accusing Madrid of creating a "false narrative" of Catalan violence and saying the pro-independence movement would "always be peaceful."

The Catalan secession movement has been a major challenge for Spain for years, triggering its biggest political crisis in decades in 2017 when the region briefly declared independence.

But it has largely been a peaceful movement characterized by mass protests.

Police said the investigation and raids targeted local groups working under the name Committees for the Defense of the Republic (CDR), which have staged periodic protests across Catalonia since separatist leaders were arrested after the 2017 independence declaration.

Police said they had seized documents, computers and materials that could be used to make explosive devices.

Those arrested were charged with rebellion, terrorism and possession of explosives, the prosecutors said.

It's said that the arrests followed a year-long investigation by the High Court.