BARCELONA, Spain — In a defiant message, Catalonia’s ousted leader, Carles Puigdemont, called on Saturday for Catalans to unite in peaceful “democratic opposition” after the Spanish central government took control of the restive region — an act Mr. Puigdemont called “premeditated aggression.”

Mr. Puigdemont said in a televised address that “our will is to continue to work to meet our democratic mandates,” in an indication that his government may attempt to ignore its dismissal and, in effect, create two competing administrations.

He spoke a day after Spain’s prime minister, Mariano Rajoy, fired him and the entire Catalan cabinet and set a date for new regional elections.

Madrid’s hard-line stance was announced shortly after regional lawmakers illegally declared an independent republic, setting up a showdown that escalated the biggest political crisis the country has faced in decades.