Spain said Wednesday it would take the unprecedented step of seeking to suspend Catalonia's autonomy if the region's leader does not abandon his independence bid, on the eve of his deadline to give a final answer.
Separatist leader Carles Puigdemont -- whose banned independence referendum on October 1 has sparked Spain's worst political crisis in decades -- has until 10:00 am (0800 GMT) on Thursday to tell the central government in Madrid whether or not he is declaring a split from the rest of the country.
Unless he backs down, Deputy Prime Minister Soraya Saenz de Santamaria said Madrid would trigger article 155 of Spain's constitution, a never before used measure that could allow it to take direct control over semi-autonomous Catalonia.
It could allow Madrid to suspend Puigdemont's regional government and eventually trigger new elections in Catalonia, but the move would risk further escalating a crisis that has sparked huge street rallies, rattled stock markets and deeply worried Spain's EU partners.
"All I ask of Mr Puigdemont is that he acts with good sense," Prime Minister Mariano Rajoy told parliament on Wednesday.
Puigdemont issued a cryptic "suspended" declaration of independence following the referendum, saying he wanted time for talks with the government -- a prospect Madrid has rejected.
Rajoy would need Senate approval to trigger article 155, but his conservative Popular Party has a majority there.
Jordi Xucla, a lawmaker from Catalonia's ruling coalition, told Rajoy in parliament that such a move would be "a serious mistake... its application would be difficult and questionable."
The latest escalation came after tens of thousands of people took to the streets of Barcelona on Tuesday night after a court jailed two influential Catalan separatist leaders, Jordi Cuixart and Jordi Sanchez, pending investigation into sedition charges.
Barcelona police said around 200,000 people massed in the city centre calling for the release of the pair known as the "two Jordis", who spent a second night behind bars Tuesday.
Shouting "freedom" and "independence", the crowds lit candles, turning the boulevard into a sea of flickering lights.
"They want us to be afraid so we stop thinking of independence, but the opposite will happen. There are more of us every day," Elias Houariz, a 22-year-old baker, told AFP at the rally.
Cuixart and Sanchez are the leaders of pro-independence citizens' groups Omnium Cultural and the Catalan National Assembly (ANC) respectively, which count tens of thousands of members each and have emerged as influential players in the crisis.
They are accused of whipping up major demonstrations last month in the run-up to the referendum, when protesters blocked Spanish police for hours inside the Catalan administration's offices as they were raiding the building.
Manchester City's Catalan manager Pep Guardiola dedicated his team's 2-1 win over Napoli in the Champions League on Tuesday to the detained pair.
"We have shown in Catalonia that citizenship is bigger than any ideas. We hope they will be released soon," he said.
Thousands of workers in Barcelona and other cities had also staged a brief walkout earlier Tuesday in protest at the detentions.
Catalan police chief Josep Lluis Trapero has also been charged with sedition -- a crime that carries up to 15 years' jail time -- accused of failing to stop the referendum going ahead.
With its own language and culture, Catalonia is proud of its autonomy but its 7.5 million people are deeply divided over independence.
Puigdemont claims the referendum resulted in a 90 percent "Yes" vote, but the turnout was only 43 percent as many supporters of Spanish unity stayed away.
Separatists argue that wealthy Catalonia, which represents about a fifth of Spain's economic output, does too much to prop up the rest of the country and would be better off going it alone.
But opponents say the region has more clout as part of a bigger Spain and that the instability could be disastrous for its economy.
Madrid announced Monday that it was cutting its economic growth forecast for next year from 2.6 to 2.3 percent, pointing blame at the Catalan crisis.
The standoff has sparked a business exodus, with nearly 700 companies moving their legal headquarters out of Catalonia in a bid to minimise the instability.