Spain’s showdown with Catalonia’s separatist leaders moved Monday to German courts as the region’s former president, Carles Puigdemont, embarked on what could be a weeks-long effort to avoid extradition from Germany.

A court in the northern town of Neumuenster ruled that Puigdemont, who was arrested Sunday in Germany, has to remain in custody for the length of the extradition proceedings.

The court said the formal requirements to detain Puigdemont had been met by a European arrest warrant issued by Spain.

In denying him bail, the court said Puigdemont posed a flight risk, concluding that he had “a strong incentive” to try to travel to Belgium where his chances of avoiding extradition might be greater.

Schleswig Holstein state prosecutor Georg Guentge said the former Catalan leader appeared “calm and composed” during Monday’s hearing, at times making legal arguments on his own behalf.

Guentge said Puigdemont can challenge the legal basis for Spain’s extradition request during the formal proceedings, which will now take place before the upper court in nearby Schleswig. Guentge said it isn’t clear whether a decision on the extradition request will happen this week and in the meantime Puigdemont will remain at the prison in Neumuenster.

With tensions flaring back home, Spain’s government said Puigdemont’s arrest at a highway rest area south of the German-Danish border during an attempt to drive from Finland to Belgium shows that “nobody can infinitely mock justice.”

Tens of thousands protested late Sunday in Barcelona and other Catalan towns, and some…