BARCELONA, Spain — Hours after the Spanish authorities announced that they would seek to prosecute Catalonia’s separatists for rebellion, Carles Puigdemont, the region’s dismissed leader, turned up on Monday in Belgium, where he may seek asylum.

Mr. Puigdemont’s reputation for unpredictability has grown with every turn of Catalonia’s secessionist drama. On Monday, he all but disappeared as the Madrid central government began using emergency laws to take over direct administration of Catalonia after its declaration of independence last week.

Speculation had mounted as to what he was up to over the course of the day, until a lawyer in Belgium finally ended the mystery surrounding Mr. Puigdemont’s whereabouts late Monday.

“I have been consulted by Puigdemont and he asked me to protect his interests in the future in Belgium,” said Paul Bekaert, a Flemish lawyer.