Catalan separatist leader Carles Puigdemont joined the European Parliament in Strasbourg on Monday and denounced Spain, which has issued a warrant for his arrest, for continuing to detain a former ally.
"There is one European Union member state, Spain, that does not respect... the European rule of law," he declared as arrived to take up his seat as an MEP, accusing Madrid of illegally detaining Oriol Junqueras.
Spain has accused both Puigdemont and Junqueras of sedition for their part in organising a banned 2017 independence referendum in the Catalan region.
While Puigdemont chose self-imposed exile in Belgium, Junqueras was detained in Spain and convicted in October. He is now serving a 13-year jail sentence.
But both men were elected to the European Parliament in last May's elections.
Last month, the European Court of Justice ruled that MEPs enjoy immunity from prosecution at the moment they are elected, leading to calls for Junqueras to be freed and Puigdemont to be allowed to sit as an MEP.
But the European Parliament followed the Spanish Supreme Court decision and removed Junqueras' mandate, leaving him in jail.
On Monday, parliamentary speaker David Sassoli allowed Puigdemont and another ally Toni Comin to take their seats, but MEPs said they were examining a request from Spain that they too lose their immunity.
If parliament decides to strip Puigdemont of his immunity, the Catalan could find himself subject to Spain's European arrest warrant.
Puigdemont missed the opening session of the parliament in July last year while still not recognised as an MEP, fearing arrest if he travelled into France to reach the Strasbourg assembly.
But on Monday, buoyed by the ECJ ruling, he dared make the short cross-border trip and he said he was no longer worried about travelling.
"We have immunity and not only in France. We also have immunity in Spain and if Spain does not respect this immunity, this will mean again that Europe begins in the Pyrenees," he said in reference to the arrest warrant in force in Spain.
- 'Take it easy' -
Puigdemont was greeted by a crowd of Catalan well-wishers, but in the chamber some right-wing Spanish deputies tried to protest.
Jorge Buxade, the head of VOX in the European Parliament, shouted his intention to intervene in the plenary, an attempt that Sassoli nipped in the bud. "Sit down, Your Honour. Take it easy," urged the speaker, an Italian socialist.
If MEPs do decide to lift immunity, in a process that usually takes weeks or even months, an examination of the extradition that Belgium suspended in January could be reactivated.
Catalonia's attempted secession triggered a crisis in Spain, which the newly formed coalition government in Madrid led by Prime Minister Pedro Sanchez is seeking to defuse through talks with the regional government.