A Spanish Supreme Court judge has ordered five Catalan separatist leaders, including the latest candidate for regional president, to be detained without bail pending their trials.
The leaders are charged with rebellion, along with eight others, over their involvement in a push for independence.
The judge said that the five were serious flight risks.
Two separatist leaders wanted by Spanish authorities are in self-imposed exile in Belgium and Switzerland.
The latest detentions throw into doubt a planned second vote in the Catalan parliament on Saturday on whether to install Jordi Turull, now in prison, as regional president.
Altogether 25 separatists have been charged, variously with sedition, rebellion, embezzlement and other crimes. They deny all the allegations.
The escalated legal action against the separatists follows Catalonia’s independence referendum last October, which the Spanish courts declared illegal.
What next for Catalonia’s independence movement?
Danny Aeberhard, Europe Regional Editor
This is the most serious challenge to date for the Catalan independence movement. Almost the entire leadership faces a major legal fight.
The legal rulings have provoked a furious response from Catalan separatists and thousands have turned out to demonstrate.
One of the accused – the sacked former head of the Catalan government, Carles Puigdemont – called Spain anti-democratic and an embarrassment to Europe. A European arrest warrant has been reactivated against him, and issued for five others who are also in self-imposed exile.