Protesters lit a bonfire on a major road and burned pictures of the king. Some banged on kitchen pots and chanted "Catalonia has no king!".

The region has been hit by weeks of protests triggered by the jailing of separatist leaders last month.

The unrest comes days before Spain's second general election this year.

Sunday's poll aims to break the stalemate that emerged from the last one in April.

Ahead of the vote, the five main party leaders outlined their positions on the Catalan crisis in a live TV debate on Monday.

Acting Prime Minister Pedro Sánchez said that if his Socialist party were re-elected, he would change the law to make it clear that organising an unsanctioned independence referendum was a serious crime.

The leader of the main opposition People's Party, Pablo Casado, said he would lead a conservative government "whose legs don't shake" when it comes to addressing the separatist issue.

The far-right Vox party leader, Santiago Abascal, went further and called for Catalan president Quim Torra to be "arrested, handcuffed and brought before the courts".

Demonstrators on Monday were joined by members of the three main separatist parties, while the separatist-led Catalan administration urged supporters to maintain restraint.

Regional leaders of parties that want to keep Spain united held a smaller counter-demonstration.

The king - along with his wife, Queen Letizia, and their two daughters - was taking part in an awards ceremony for young entrepreneurs, scientists and artists.

Heir to the throne, Princess Leonor, 14, gave a speech at the ceremony, stressing her attachment to Catalonia.

"This land, Catalonia, will always hold a special place in my heart," she said in her address given in Spanish and Catalan.

The awards venue in Barcelona was heavily guarded by police who set up barricades and blocked one of the city's main thoroughfares.

BBC

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