MADRID -- Spain's prime minister on Wednesday urged Catalonia's leaders to back down from their bid to gain independence for the region, a day before a central government deadline that could significantly deepen the country's political crisis.

Prime Minister Mariano Rajoy has given Catalan president Carles Puigdemont until Thursday morning to clarify whether he is making the wealthy region independent. The Madrid-based national government is threatening to take the unprecedented step of seizing some or total control of the semi-autonomous region if Puigdemont proceeds with his ambitions of secession. That would likely trigger an explosive reaction in Catalonia.

With the clock ticking, Rajoy called on Puigdemont to "act sensibly" and heed the interests of all Spaniards and Catalans.

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Addressing Puigdemont's party lawmakers in the Spanish parliament, Rajoy said they should try to convince the Catalan leader "not to make any more problems."

The tension remained high, however, just weeks after an Oct. 1 referendum in Catalonia which Spain's top court ruled was unconstitutional.

About 50 Spanish and Catalan party lawmakers held up posters in parliament demanding the release of two pro-Catalonia independence movement leaders, describing them as political prisoners.

Lawmakers hold up posters reading: "Free Jordi Sanchez and Jordi Cuixart," leaders of the Catalan grassroots organizations Catalan National Assembly and Omnium Cultural, during a parliamentary session at the Spanish parliament in Madrid, Oct. 18, 2017. AP

The protest lasted around 15 seconds before the lawmakers heeded warnings that they were out of order and sat down.

The demonstration was over Monday's jailing of Jordi Sanchez and Jordi Cuixart, leaders of the Catalan grassroots organizations Catalan National Assembly and Omnium Cultural, in a sedition investigation. Tens of thousands of people demonstrated Tuesday in Catalonia, demanding their release.