People gather to protest a court decision to imprison civil society leaders without bail in Barcelona on Oct. 17, 2017. (Emilio Morenatti/AP)

Spain and the secessionist leaders in Catalonia were headed toward an ever-more-serious showdown following the central government’s announcement Thursday that it would move quickly to assert control of the autonomous region after its president refused to end his push for independence.

Facing a deadline imposed by Spain’s central government to say whether Catalonia was declaring independence, the regional president replied Thursday that Madrid should stop threatening Catalonia and instead agree to dialogue to end the impasse.

Catalan President Carles Puigdemont answered Spain’s demand for clarity by sending a second letter to Prime Minister Mariano Rajoy, stating that Catalonia’s suspension of its declaration of independence remains in force — for the moment.

Puigdemont then added a threat of his own: If Madrid does not agree to talks and continues its “repression” of the region, the Catalan parliament will meet soon to vote on a formal declaration of independence.

The Spanish government moved Oct. 19 to begin procedures to take control of Catalonia. (The Washington Post)

The Catalan government’s decision to effectively decline to respond to Madrid’s ultimatum brings Spain to the brink of a constitutional crisis.

The central government in Madrid responded that it would begin the process of implementing Article 155 of Spain’s 1978 constitution, which allows it to take over the regional government, including its finances and police. Madrid announced a meeting of ministers for an “extraordinary” session Saturday where they would define what such a takeover would entail and how to achieve it.

Such a move would be unprecedented in Spain’s four decades since the end of the Francisco Franco dictatorship.

People in Catalonia — and around Spain — braced for what would come next.

This is uncharted territory.

“Nobody knows what Article 155 means, because no one has ever invoked it before,” Oriol Junqueras, the vice president of the Catalan regional government, told The Washington Post.

Referring to the central government in Madrid, he said, “they don’t know what they want to do with this.”

Asked if he could imagine authorities entering his office and arresting him, the vice president answered, “The national police and the [paramilitary] Guardia Civil have already been in this building, where they detained 14 public workers and officers. They’ve jailed leaders of civil society organizations. So yes, I can imagine this happening.”

The head of the Ciudadanos party, Albert Rivera, who favors implementing Article 155, told reporters in Madrid that “a European democracy cannot be blackmailed” by the Catalan government.

José Luis Ábalos, a leader of the Socialists, who serve as the opposition in the Spanish parliament, told El Pais newspaper that his party wants the enactment of Article 155 to be “very, very limited” and to last “the shortest period of time possible.” But he said it was necessary to preserve the rule of law.

Pro-independence activists in Catalonia went into rushed meetings Thursday to organize mass demonstrations, distribute instructions for peaceful civil disobedience and plan to surround government buildings.

There was widespread anxiety in Barcelona over possible clashes between national police, sent to enforce a takeover, and pro-independence demonstrators.

The chief of Catalonia’s regional police, Josep Lluís Trapero, already has been questioned by prosecutors over his alleged failure to protect federal forces sent into the region. Two other pro-independence activists have been jailed on suspicion of sedition. Puigdemont called them “political prisoners.”

Rajoy has warned that if Catalonia declares independence, he will seek permission from the upper house of the Spanish legislature, where his party has a majority, to enact Article 155.

Catalonia, a wealthy state in northeastern Spain that has a population of 7 million and its own language and culture, already enjoys substantial control over its affairs. The regional government holds sway over health care, education, media and local police.

If Madrid enacts Article 155, Rajoy could appoint his own deputies to steer the regional government’s ministries. It is unclear what would happen to Puigdemont. He could remain in his position as regional president but would be effectively powerless.

This month, Catalonia staged a chaotic independence referendum marked by widespread civil disobedience. It was met by a harsh response in which national police and Guardia Civil officers beat voters with rubber batons and dragged away ballot boxes.

The central government, backed by the courts, had declared the referendum illegal and unconstitutional.

Still, many in Catalonia demanded the right to vote and saw Madrid as callously disregarding the people’s will. Although many polling stations were raided by police, more than 2 million people managed to vote — and 90 percent chose independence.

Critics charge that the referendum was hopelessly compromised, not only by riot police and legal challenges but by low turnout — only 40 percent of eligible voters cast ballots.

After the Oct. 1 referendum, Puigdemont signed an independence declaration. But then he immediately suspended it, saying Catalonia wanted to negotiate with the central government, with help from Europe.

Leaders in Europe condemned the staging of the referendum and the police tactics, stressing that it was an internal matter for Spain and that they would not recognize Catalonia as an independent nation and a member of the European Union.

When Spain’s prime minister spoke Wednesday at the national parliament in Madrid, he was clearly frustrated.

“The only thing I am asking Mr. Puigdemont is that he act sensibly, that he act with balance, that he puts first the interests of all citizens, of all Spaniards and all Catalonians,” Rajoy said.

The central government has given Puigdemont several deadlines to declare whether the Catalan authorities were proclaiming independence.

On Monday, the first deadline, Puigdemont wrote a letter to Rajoy, calling instead for two months of dialogue and a halt to what he called Spain’s “repression” of Catalan citizens and institutions.

Rajoy said in parliament Wednesday: “It’s simple, and it’s not that difficult. It’s answering one question: Have you or have you not declared the independence of Catalonia? Because you understand if you have declared the independence of Catalonia, the government is obliged, because that is what it says in the constitution, that it must act in a certain way.”

Some leaders in Madrid said that Catalonia should suspend its declaration of independence and immediately move toward regional elections.

It is not clear what such elections would solve. It is possible that pro-independence sentiment has only grown in Catalonia in recent weeks.

Raul Gallego Abellan contributed to this report.