The former Catalan government head Carles Puigdemont has been detained by Italian police in Sardinia, his office said in a statement.
Mr Puigdemont was detained when he travelled to the city of Alghero from Brussels to attend the Adifolk International Exhibition and to meet with the regional head of Sardinia and its ombudsman.
Spain has accused the Catalan separatist leader of sedition, claiming he helped organise a 2017 independence referendum deemed illegal by Spanish courts.
In March, the European parliament stripped Mr Puigdemont and two of his former ministers of parliamentary immunity.