A former Catalan leader sought by Spain for a failed secession bid is due in court to argue against extradition, a day after Italian police detained him in Sardinia, an Italian island with strong Catalan cultural roots and its own independence movement.

Police on Thursday night transferred Carles Puigdemont to a jail in the city of Sassari after he was detained at the airport in Alghero on an international warrant.

Alghero is hosting a traditional Catalan folklore festival that he was expected to attend.

Demonstrators outside the courthouse in Sassari held signs in a Sardinian dialect proclaiming “Democracy, the Sardinian nation supports the Catalan nation”, and carried the flags of Sardinia and Catalonia — the north-eastern Spanish region for which Puigdemont pushed for secession from Spain.

Demonstrators hold Sardinian and Catalonian flags
Demonstrators hold Sardinian and Catalonian flags (Gloria Calvi/AP)

His Italian lawyer, Agostinangelo Marras, told reporters outside the courthouse that an appeal court judge will hold a hearing to either uphold Puigdemont’s detention or release him, as part of the extradition request process.

The judge’s decision “will be based on documents that I and the judge will have to evaluate”, the lawyer said.

The hearing might be held later on Friday or perhaps on Saturday morning, the lawyer indicated.

Ultimately, it will be up to the Italian justice ministry to approve or deny extradition.

At the heart of the immediate legal matter is whether the warrant issued by Spain seeking his arrest is valid. His lawyer in Spain, Gonzalo Boye, insisted the warrant issued in 2019 has been suspended.

Mr Boye told Spanish radio station SER: “We have to see whether the arrest warrant is enforceable. That’ll be up to the legal authorities” in Italy.

Spain’s Supreme Court, which issued the European arrest warrant, made no official comment.

It is not the first time Spanish courts have tried to detain Puigdemont abroad. After a Belgian court declined to send him back in 2017, the following year he was arrested in Germany but a court there also refused to extradite him.

Puigdemont and a number of his separatist colleagues fled to Belgium in October 2017, fearing arrest after holding an independence referendum for Catalonia that the Spanish courts and government said was illegal.

Nine Catalan separatists later received prison sentences for their role in the 2017 referendum ranging from nine to 13 years. They were pardoned in July but Puigdemont, who fled, was not.

He holds a seat in the European Parliament, although that legislature stripped him of parliamentary immunity.

Carles Puigdemont at the European Parliament in Brussels
Carles Puigdemont at the European Parliament in Brussels (Francisco Seco/AP)

The Spanish government said Puigdemont’s detention in Sardinia “obeys a legal process which is under way and which applies to any citizen of the European Union who must respond to his acts in court”.

Madrid said it would respect decisions taken by Italian authorities and its courts.

Earlier in the week, Sardinian media reported that Puigdemont had been invited to a closed-door gathering in Oristano, Sardinia, of sympathisers of a Sardinian independence movement.

Alghero’s historic and cultural ties with Catalonia date back to the 14th century, when a Catalan-Aragonese force won a naval battle off the Sardinian coast and the forces’ commander entered triumphantly into the city on Sardinia’s north-west coast.

Some 20% of Alghero’s residents speak a Sardinian dialect derived from the Catalan tongue and recognised by the national government of Italy and the island’s regional government.

The Catalan regional government keeps a delegation in Alghero, which is now a popular tourist town.