Catalan separatist leader Carles Puigdemont was detained on Thursday by Italian police in Sardinia, his office said in a statement.
Spain has accused Puigdemont, the former Catalan regional head, with sedition, claiming he helped organise a 2017 independence referendum deemed illegal by Spanish courts.
In March, the European Parliament stripped Puigdemont of the immunity he enjoyed as a member since 2019. Puigdemont was living in self-imposed exile in Belgium.
His office said Puigdemont had travelled to Alghero on Thursday afternoon from Brussels to attend the Adifolk International Exhibition and to meet with the regional head of Sardinia and its ombudsman.
"When he arrived at the Alghero airport, he was stopped by the Italian border police. Tomorrow he will be placed at the disposal of the judges of the court of appeal of Sassari, which is competent to decide whether to release him or extradite him," Puigdemont's office said in the statement.
His lawyer Gonzalo Boye confirmed the detention in a tweet, adding that it was made on the basis of a European arrest warrant from Oct. 14, 2019, which, by "legal imperative - as stated by the European Court of Justice, is suspended."
Puigdemont was subject to a European arrest warrant issued by Spain which is seeking his extradition over his role in the independence bid.
The referendum brought on Spain's biggest political crisis in decades and was followed by a unilateral declaration of independence by the Catalan parliament in October 2017, which prompted the central government to impose direct rule from Madrid and authorities to arrest separatist leaders.
"Mr. Puigdemont must submit to the action of the courts, exactly like any other citizen," Spanish Prime Minister Pedro Sanchez's office said in a statement.
He is due to attend an Italian court on Friday morning, though it is unclear whether the judge will decide whether he should be extradited, Italian news wire ANSA reported.
"We believe that the judicial authorities will release Puigdemont. This is the fourth time this has happened," his lawyer Gonzalo Boyer told on Friday Cadena Ser radio.