Spain's high court ordered two top Catalan separatists jailed for alleged sedition while the question of the region's independence remains unclear.
Prosecutors accuse Jordi Cuixart of the Omnium Cultural movement and Jordi Sanchez of the Catalan National Assembly of provoking violence against police during a pro-independence march last month.
Protesters trapped officers inside a building and destroyed several police cars.
"Spain jails Catalonia's civil society leaders for organizing peaceful demonstrations," Catalan President Carles Puigdemont tweeted Monday. "Sadly, we have political prisoners again," an apparent reference to Francisco Franco's military dictatorship that ended more than 40 years ago.
The High Court also placed Catalan police chief Josep Lluis Trapero under investigation. The court declined to order him behind bars, but did revoke his passport to keep him from leaving the country.
Meanwhile, Puigdemont has still not said whether he will declare Catalan independence outright after the court and Spanish government declared a pro-independence referendum illegal.
Puigdemont had a Monday deadline to give a simple "yes" or "no" answer to the question whether he will declare independence. So far, he has only called for talks with Spanish Prime Minister Mariano Rajoy and the deadline has been pushed to Thursday.
A frustrated Rajoy has said the uncertainty surrounding Catalonia is hurting the Spanish economy. The economic ministry Monday cut its economic growth forecast for 2018 because of the crisis.
Catalonia, Spain's most prosperous region, is home to 7.5 million people. Its capital, Barcelona, is one of Europe's major tourist attractions. Catalonia has its own language and distinct culture, and is deeply divided over independence.
The Catalan government said that 90 percent of Catalans voted for independence from Spain in the October 1 referendum. Many opponents of independence boycotted the vote, reducing turnout to around 43 percent.
VOA's Isabela Cocoli contributed to this report.