MADRID — In a first for Spain, Prime Minister Mariano Rajoy announced on Saturday that he would remove the separatist government of the independence-minded region of Catalonia and initiate a process of direct rule from Madrid. The announcement, made after an emergency cabinet meeting, was an unexpectedly forceful attempt to stop a yearslong drive for secession in Catalonia, which staged a highly controversial independence referendum on Oct. 1, even after it was declared illegal by the Spanish government and courts. Mr. Rajoy took the bold steps with broad support from Spain’s main political opposition, and will almost certainly receive the required approval next week from the Spanish Senate, where his own conservative party holds a majority. But the moves were immediately condemned by Catalan leaders and thrust Spain into uncharted waters, as the prime minister tried to put down the gravest constitutional crisishis country has faced since embracing democracy after the death of its dictator Gen. Francisco Franco in 1975. It would be the first time that the central government in Madrid has stripped the autonomy of one of its 17 regions, and the first time that a leader has invoked Article 155 of the Spanish Constitution — a broad tool intended to protect the “general interests” of the nation. Mr. Rajoy said the Catalan government had never offered real dialogue with the central government in Madrid but had instead tried to impose its secessionist project on Catalan citizens and the rest of the country in violation of Spain’s Constitution. He said his government was putting an end to “a unilateral process, contrary to the law and searching for confrontation” because “no government of any democratic country can accept that the law be violated, ignored and changed.” Mr. Rajoy said he planned to remove the Catalan leader, Carles Puigdemont, and the rest of his separatist administration from office. The central government was also poised to take charge of Catalonia’s autonomous police force. Mr. Rajoy did not ask to dissolve the Catalan Parliament, but instead said that the president of the assembly would not be allowed to take any initiative judged to be contrary to Spain’s constitution for a period of 30 days, including trying to propose another leader to replace Mr. Puigdemont. Mr. Rajoy said that his goal was to arrange new Catalan elections within six months, so as to lift the measures taken under Article 155 as soon as possible. However, it’s unclear how such elections would be organized or whether they would significantly change Catalonia’s political landscape, let alone help to resolve the territorial conflict. In fact, the steps announced by Mr. Rajoy run a serious risk of further inflaming an already volatile atmosphere in Catalonia, where tens of thousands braved Spanish national police wielding truncheons to vote for independence during the barred Oct. 1 referendum. Mr. Puigdemont was expected to lead a mass demonstration in Barcelona, the region’s capital, on Saturday afternoon, before giving his official response to Mr. Rajoy’s decision. Protests in Barcelona on Saturday VIDEO BY LA VANGUARDIA Several Catalan separatist politicians, however, reacted immediately to Mr. Rajoy’s announcement, warning that it would escalate rather than resolve the conflict. Josep Lluís Cleries, a Catalan senator, told reporters on Saturday that Mr. Rajoy’s decision showed that “the Spain of today is not democratic because what he has said is a return to the year 1975,” referring to Franco’s death. Mr. Rajoy, he added, was suspending not autonomy in Catalonia but democracy. Oriol Junqueras, the region’s deputy leader, said in a tweet that it was “facing totalitarianism” and called on citizens to join the Barcelona protest on Saturday. Significantly, Iñigo Urkullu, the leader of the Basque region, which also has a long history of separatism, described the measures as “disproportionate and extreme,”writing on Twitter that they would “dynamite the bridges” to any dialogue. Faced with Madrid’s decision to remove him from office, Mr. Puigdemont could try to pre-empt Mr. Rajoy’s intervention and instead ask Catalan lawmakers to vote on a declaration of independence in coming days — as he had threatened to do earlier this month. Mr. Puigdemont could also then try to convene Catalan elections, on his own terms, to form what he could describe as the first Parliament of a new Catalan republic. Should Mr. Puigdemont resist Mr. Rajoy’s plans, Spain’s judiciary could separately step in more forcefully and order that he and other separatists be arrested on charges sedition or ultimately even rebellion for declaring independence. Rebellion carries a maximum prison sentence of 30 years. Earlier this week, a judge from Spain’s national court ordered prison without bail for two separatist leaders, pending a sedition trial. Using Article 155 “was neither our desire nor our intention,” Mr. Rajoy said on Saturday, but had become the only way to to return Catalonia to legality, normality and maintain a Spanish economic recovery “which is now under clear danger because of the capricious and unilateral decisions” of the Catalan separatist government. Mr. Rajoy highlighted the decision of over 1,000 Catalan companies this month to relocate their legal headquarters outside the region, in response to the uncertainty generated by the possibility of breakup/break up with Madrid. Mr. Rajoy received strong backing from politicians from the main opposition parties, with the notable exception of Podemos, the far-left party that wants to use a referendum to convince Catalan voters to remain within Spain. “We’re shocked by the suspension of democracy in Catalonia,” Pablo Echenique, a senior official from Podemos, said in a televised news conference on Saturday, after Mr. Rajoy’s announcement.