BARCELONA, Spain — Catalan separatists vowed Saturday to ignore a police ultimatum to leave the schools they are occupying to use in a vote seeking independence from Spain.

As police sealed off hundreds of schools, some parents decided to send their children home and girded for pre-dawn confrontations Sunday with police.

Tensions rose across the country over the planned vote. In Madrid, the Spanish capital, thousands marched to protest the separatists’ attempt to break up their nation, demanding that Catalan leaders be sent to jail. In Barcelona, the capital of Catalonia, thousands more also took to the streets to urge their prosperous region to stay united with Spain.

The police deadline of 6 a.m. Sunday for the activists, parents and children in the occupied Catalan schools is designed to prevent the vote from taking place, as polls are supposed to open three hours later.

Spain’s Constitutional Court suspended the independence vote more than three weeks ago, and the national government calls it illegal. Police have been ordered to stop ballots from being cast Sunday and have been cracking down for days, confiscating millions of ballots and posters.

But Catalonia’s defiant regional government is pressing ahead, urging the region’s 5.3 million voters to make their voices heard.

Spain’s foreign minister dismissed the planned vote as anti-democratic, saying it runs “counter to the goals and ideals” of the European Union. “What they are pushing is not democracy. It is a mockery of democracy, a travesty of democracy,” Alfonso Dastis told The Associated Press in an interview.

He accused some pro-independence groups of “adopting Nazi-like attitudes by pointing at people that are against that referendum and encouraging others to harass them.”

Spain’s Interior Ministry said police had sealed off “most” of the region’s 2,315 polling stations and disabled software being used in the referendum. Enric Millo, the highest-ranking Spanish official in the northeastern region, said parents and students were occupying at least 163 schools by mid-Saturday, when about 1,000 more still needed to be checked.

In a later update, the ministry didn’t provide a new figure but said “some” schools remained occupied.

The regional police force has been ordered not to use force in vacating the schools, but Millo said anyone remaining after 6 a.m. will need to be removed.

“I trust in the common sense of Catalans and that people will operate with prudence,” he said.

Authorities have already confiscated 10 million paper ballots in the last few days — which will make it much more difficult for Catalan officials to carry out an effective vote.

Millo said the Spanish government would tolerate ad hoc voting in the streets but that those results could not be considered valid.

The main civic group behind Catalonia’s push for independence said — given the concentrated efforts by Spain to block the vote — that a turnout of 1 million voters, less than a fifth of the electorate, should be considered an “overwhelming success.”

The Catalan government has pledged to declare independence from Spain within 48 hours of Sunday’s vote if the ‘yes’ side wins, regardless of turnout.