Stepping up pressure on the Catalan government, he has given Carles Puigdemont, the Catalan president, five days to clarify the suspended declaration of independence he made on Tuesday.
Mr Rajoy said his formal request for clarity was “necessary when activating Article 155” and would dictate the next steps in the crisis to “offer certainty to the citizens”.
Using Article 155 to suspend Catalan autonomy would deepen the constitutional crisis in Spain since Catalonia held a contested referendum on independence on October 1. Spain’s government says Catalonia’s independence drive is unconstitutional.
Mr Puigdemont on Tuesday night stepped back from making a full declaration of immediate independence, calling for more dialogue with Spain to peacefully resolve the matter. But his speech to the Catalan parliament was ambiguous.
At one point he appeared to declare independence, saying he now assumed the “mandate for Catalonia to become an independent state in the form of a republic”. But this was followed by a proposed suspension of independence for a “few weeks”.
According to Spanish media, Madrid has given Catalonia until Monday to confirm its independence. The regional government would then be given three more days to rectify its decision before Article 155 would be triggered next Thursday.
Meanwhile, there were signs that the government was trying to take some steps to de-escalate the situation.
Pedro Sanchez, the head of the opposition socialists, said on Wednesday that his party and the ruling centre-right PP party had agreed to talks to renegotiate laws governing regional autonomy.
He said there would be six months of talks on reforming the constitution, followed by a debate in parliament, adding that his party wanted a constitutional reform to “allow for Catalonia to remain a part of Spain”.
Mr Sanchez also said his party was backing Mr Rajoy’s calls for clarification over what Mr Puigdemont said on Tuesday night.
Addressing parliament on Wednesday evening, Mr Rajoy rejected offers of international mediation in the Catalonia crisis, and called for respect of Spanish law.
He said there was “no possible mediation between democratic law and disobedience and unlawfulness”. He also described the crisis as “one of the most difficult times in our recent history”.
European Commission vice-president Valdis Dombrovskis said that Catalonia’s separatist authorities have appealed to Brussels to help mediate with Madrid but Mr Rajoy has not sought EU help.
“The commission is following closely the situation in Spain, and reiterates its earlier call for full respect of the Spanish constitutional order,” he said. “We are supporting the efforts to overcome division and fragmentation, to ensure unity and respect of the Spanish constitution.”
German chancellor Angela Merkel’s deputy spokeswoman said any independence declaration by Catalonian institutions would be “illegal and unacceptable and would find no recognition” in Germany.
Alfonso Dastis, Spain’s foreign minister, said Mr Puigdemont’s speech amounted to a “trick to say one thing and do the opposite”, without giving further details of the government’s plans.
Mr Puigdemont’s announcement came after his government said that more than 2m people voted in the referendum, most of them favouring independence. Catalonia has more than 5.3m eligible voters.
Under a law passed by the Catalan parliament in the weeks before the referendum, the parliament would declare independence within 48 hours of a Yes vote.
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