Spain's King Felipe VI has condemned the Catalan authorities, saying they placed themselves "outside the law" by holding an independence vote Sunday.
In a television address to the nation Tuesday, the king called for unity even as thousands took to the streets across Spain's northeastern province to protest a Spanish police crackdown during the referendum.
Separatist Catalan leaders have vowed to declare independence even though Madrid has declared the vote illegal and invalid. Catalan leader Carles Puigdemont told the BBC such a declaration could come within days.
Catalan labor unions called for a general strike to voice anger about the treatment by Spanish police of people trying to vote in the region's independence referendum.
The strike affected affected bus and subway services, schools, shops and other businesses. Spain's famous Barcelona soccer team said it would join in the strike, and it suspended operations at its club headquarters for the day.
Officials in Catalonia said nearly 900 people were injured when police tried to keep residents from voting in the referendum, which was deemed unconstitutional by Spanish courts.
Video from Sunday showed police dragging people from polling stations and beating and kicking would-be voters and demonstrators.
Amnesty International said its observers witnessed "excessive use of force" by Spanish police.
The top Spanish official in the Catalan region, Enric Millo, said Tuesday that he regretted the violence that left so many people injured, but he blamed Catalan officials for "exposing citizens to danger."
He added, "Nothing of this would have happened if the government wouldn't have declared itself in rebellion, breaking the orders of the courts and lying and tricking people."
He said Spanish police broke into schools being used as polling stations only after local police failed to carry out a judge's order to stop the vote.
European Union chief Donald Tusk appealed to Spanish Prime Minister Mariano Rajoy on Monday to "avoid further escalation and use of force" in the standoff.
Officials in Catalonia said 90 percent of those who voted in the referendum chose independence from Spain, and they called for international mediation to solve the political deadlock.
Spain will do "everything within the law" to prevent Catalonia from declaring independence, Justice Minister Rafael Catala said Monday in an interview with Spanish public television.