BARCELONA, Spain - Protesters backing Catalonia's secession from Spain clashed with police and blocked major roads and train tracks across the northeastern region on Thursday during a strike called to protest the trial of a dozen separatist leaders.

Regional police say they made three arrests when they met resistance trying to clear groups of protesters who had stopped traffic.

One protester was arrested for hitting an officer in downtown Barcelona, police said. A second arrest was made on a highway north of Barcelona where protesters threw objects at a line of riot police. A third was made south of Barcelona.

Twelve officers also received minor injuries in the clashes, according to police. Protesters threw rocks at police lines and burned tires on some highways.

Regional transportation authorities said the disruptions affected main thoroughfares in Barcelona and half a dozen major highways and railway tracks elsewhere in Catalonia.

The general strike was organized by small unions of pro-independence workers and students. On paper, they were demanding improved social policies including a 35-hour work week and a higher minimum wage, but the protesters carried pro-secession flags and chanted slogans for the release of the 12 separatists currently on trial in the Madrid-based Supreme Court.

The main unions in Catalonia did not back the strike, which appeared to have a limited impact on businesses.

In Barcelona, students in favour of secession held a march. The pro-secession grassroots group ANC - whose protest slogan is “self-determination is not a crime” - was planning a separate march later Thursday.

The Spanish government says regions cannot independently secede, according to the Constitution.

The trial into the roles played by the 12 separatists in Catalonia's failed 2017 secession attempt is in its second week. On Thursday, former Catalan government member Santi Vila, ANC's ex-president Jordi Sanchez and fellow activist Jordi Cuixart were scheduled to testify at the court. The trial is expected to last at least three months.

Election results and polls indicate that Catalonia's 7.5 million residents are divided down the middle over the secession issue.