Catalonia will move to declare independence from Spain on Monday (9 October), a regional government source has said.
Pro-independence parties which control the Catalan government have called for an independence vote at the start of the week, the source told Reuters, adding that a declaration would follow the vote.
Spain's King Felipe VI denounced the referendum for "showing disrespect to the powers of the state."
"They have broken the democratic principles of the rule of law. Today, the Catalan society is fractured," he said during a televised address.
Catalan President Carles Puigdemont told the BBC on Tuesday (3 October) that if the Spanish government tries to intervene in Catalonia's independence declaration, it would be an "error which changes everything."
Some 90% of those who cast their ballot in last weekend's independence referendum voted 'yes.' The turnout was around 42%, despite a police operation aimed at preventing hundreds of people from voting.
Ahead of the referendum, Spain's Constitutional Court declared the vote illegal and Spanish riot clashed with voters at polling stations. More than 840 people required medical treatment following the violent rallies.
The constitutional crisis in Spain, which is the fourth-biggest economy in the euro zone, has caused stocks and bonds to tumble.
Tourism and production in Catalonia fuel the Spanish economy, with the region's output totalling a fifth of Spain's GDP.