Chanting a cry of resistance from Spain's 1936-1939 civil war, thousands of mainly young people thronged this capital's emblematic Puerta del Sol square Wednesday night in defiance of a ban on demonstrations ahead of weekend regional and municipal elections.

"They will not pass," the crowd roared, repeating the famous words of Communist firebrand Dolores "La Pasionaria" Ibarruri (1895-1989) during the civil war siege of Madrid by Gen. Francisco Franco.

Demonstrators also shouted slogans expressing disgust with both the governing Socialists and the main opposition conservative Popular Party.

Police, who forcibly evicted some 150 protesters from the area early Tuesday, stood by as the activists vowed to resist peacefully if authorities tried to dislodge them.

The protesters are part of the self-styled May 15th Movement, which took to the streets of Spanish cities last Sunday to demand "real democracy now" and a new economic policy amid joblessness of more than 21 percent.

Madrid's electoral board issued an order denying authorization for protests in the days before Sunday's voting, suggesting the demonstrators' rhetoric could somehow hamper the free exercise of the franchise.

A spokesperson of the May 15th Movement asked those in the massive crowd that had gathered in the Puerta del Sol by Wednesday night to remain united and to avoid provoking the police.

"This is a peace encampment," the spokesperson said as protesters circulated flyers citing a provision of Spain's post-Franco constitution that gives citizens the right to protest without prior authorization.

Police assured the protesters they will not try to clear the square by force, May 15th Movement organizer Pablo Gomez said, though adding that authorities "have already lied other times."

Many plainclothes police have infiltrated the crowd and "there are groups that want to tear down what we have been building peacefully," Gomez said.

Similar protests are under way in other major Spanish cities, including Barcelona, Bilbao, Zaragoza and Valencia, where activists likewise vow to remain mobilized at least through the elections.

In a manifesto issued Tuesday in Madrid, the protesters call for a society that puts human dignity ahead of economic interests.

United by anger over the state of the Spanish economy and disenchantment with politicians, the May 15h Movement is made up of numerous small groups and operates largely via Internet social networks.

The effects of the global recession and the bursting of a decade-long property bubble have been particularly severe for Spanish residents under 25, who suffer a jobless rate of more than 40 percent.

Spain faces the prospect of a "lost generation," the International Monetary Fund said in a May 13 report.