Independence supporters form the word Independence during Catalonia's National Day in Barcelona, Spain, Sept 11, 2018. Hundreds of thousands Catalans have shouted in a collective roar along a main artery of Barcelona to demand independence from Spain. (ROSER VILALLONGA / ANC VIA AP)

BARCELONA, Spain — 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.

More protests are planned to mark the anniversary of the Oct 1 Catalan referendum

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.

READ MORE: Spanish, Catalan leaders meet to bridge gap over secession

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.

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

Protesters gather to mark the first year since Spanish police began searching the regional government buildings and arresting Catalan officials, in Barcelona, Spain, Sept 20, 2018. (EMILIO MORENATTI / AP)

A man holds a child covered with a pro-independence Catalan flag on his shoulders during the Catalan National Day in Barcelona, Spain, Sept 11, 2018. (SANTI PALACIOS / AP)

Regional Catalan President Quim Torra, speaks in front of protesters in Barcelona, Spain, Sept 20, 2018. (EMILIO MORENATTI / AP)

Demonstrators supporting Spanish unity march, during a demonstration in Barcelona, Spain, Sept 16, 2018. (DANIEL COLE / AP)

A demonstrator supporting Spanish unity shouts slogans towards Catalonian separatists during a demonstration in Barcelona, Spain, Sept 16, 2018. (DANIEL COLE / AP)