Prosecutors in Madrid have asked for eight sacked members of Catalonia’s regional government to be jailed over their role in October’s disputed independence referendum.
Nine Catalan officials testified at Spain’s high court over accusations of rebellion, sedition and misuse of public funds.
Ousted Catalan leader Carles Puigdemont and four others disregarded a summons.
The deposed leader, who is in Belgium, said the trial was “political”.
Spain has been gripped by a constitutional crisis since the referendum was held on 1 October in defiance of a constitutional court ruling that had declared it illegal.
Last week, Spanish Prime Minister Mariano Rajoy imposed direct rule on Catalonia, dissolving the regional parliament and calling snap local elections for 21 December.
This came after Catalan lawmakers voted to declare independence of the affluent north-eastern region.
The Catalan government said that of the 43% of potential voters who took part in the referendum, 90% were in favour of independence.
What is happening?
Spain’s chief prosecutor asked the high court judge to jail eight of the nine members who turned up for questioning.
One of them, Catalonia’s former business minister Santi Vila, should be granted a €50,000 ($58,000; £54,000) bail. He resigned before the Catalan parliament voted for independence on Friday.
The Catalan leaders are yet to be formally charged. A judge will have to decide whether the officials should go to jail, pending an investigation that could potentially lead to a trial.
The judge can also grant them conditional bail and order them to surrender their passports.
They were accused of rebellion – which carries a maximum 30-year jail term – as well as sedition and misuse of funds.
Who showed up – and who did not?
Mr Puigdemont had previously said he would not return to Spain if he and his colleagues did not receive unspecified guarantees of a fair trial.
His Belgian lawyer told Reuters news agency that he would co-operate with the authorities, but did not appear before the judges because “the climate is not good”.
The four other sacked leaders who failed to show up at the high court also stayed in Belgium. Reports suggest some of them requested to appear before the judges via videolink.
Mr Puigdemont’s handling of the crisis has drawn criticism among some other Catalan politicians, with left-wing parliamentary deputy Joan Josep Nuet saying his absence could make matters worse for those who followed the court’s order.
“The attitude… has been really absurd, managing only to create yet more bewilderment,” he told Catalunya Radio.
Among those who showed up were the sacked deputy leader Oriol Junqueras, Interior Minister Joaquin Forn, foreign affairs chief Raül Romeva and spokesman Jordi Turull.
Meanwhile, five other senior members of the Catalan parliament, as well as speaker Carme Forcadell, are facing the same charges but, because of their parliamentary immunity, their cases are being handled by the Supreme Court.
Their hearings have been postponed until 9 November.