BARCELONA, Spain (AP) — Thousands of Catalan pro-independence activists are protesting in Barcelona to mark the anniversary of demonstrations that fired up the region's secessionist drive and brought Spain's worst political crisis in decades.

The protest Thursday recalled street demonstrations that were a prelude to weeks of tension last year in Spain's wealthy northwestern region. Separatists organized a 2017 referendum on independence that was outlawed, and the Spanish government deployed police to stop the vote.

Protesters are demanding the release from prison of prominent separatists, among them Jordi Sanchez and Jordi Cuixart, the leaders of grassroots organizations Catalan National Assembly and Omnium Cultural. They have received preliminary sedition charges but no trial date has been set.

More protests are planned to mark the anniversary of the Oct. 1 Catalan referendum and a subsequent failed declaration of independence.