MADRID—Spanish Prime Minister Mariano Rajoy gave the leader of Catalonia until Thursday to cease his bid for independence or face the loss of some regional powers at the hands of the central government.

Mr. Rajoy, in a letter sent to Carles Puigdemont on Monday, said the Catalan leader hadn’t clarified whether he declared the region independent from Spain last week, as the central government had demanded in an earlier injunction. The Catalan leader now has until Thursday morning to withdraw his secessionist drive. If he doesn’t, Mr. Rajoy said he would invoke an article of the Spanish constitution that would allow the central government to strip the wealthy region of some of its powers.

“Never in their history have the citizens of Catalonia enjoyed greater liberty and political and financial autonomy than in this democratic period. The only conflict that exists at this moment in Catalonia is a conflict of lawfulness,” Mr. Rajoy said in the three-page letter addressed to Mr. Puigdemont. The prime minister called on the Catalan leader to respect the rule of law and drop his bid to split with Spain.

Last week, Mr. Rajoy gave Mr. Puigdemont until Monday at 10 a.m. local time to set the record straight on whether he declared the region independent. Anything but an unequivocal statement denying that was his intent would be taken as a proclamation of Catalonia’s secession from Spain, according to an injunction Madrid sent to the Catalan leader on Wednesday.

In a response sent to Mr. Rajoy earlier Monday, Mr. Puigdemont didn’t say whether he declared the wealthy Spanish region an independent republic during his earlier speech, but called for a meeting “as soon as possible” with the prime minister to discuss Catalonia’s future. Mr. Rajoy has steadfastly refused to enter into talks on Catalonia’s secession because he says it violates Spain’s constitution.