SPANISH prime minister Mariano Rajoy said his government will announce specific measures tomorrow to take control of Catalonia, now that an agreement has been reached with the country's main opposition parties.

Rajoy refused to confirm if the agreement with the Socialists includes plans to force through a new election in Catalonia in January.

This would be done through powers not used since democracy was restored in Spain, and was announced by the party's negotiator earlier.

Rajoy, commenting on the unprecedented constitutional step he is taking to seize control of Catalonia, said: "The goal is double: the return to legality, and the recovery of institutional normalcy."

The prime minister said the Catalan crisis was only discussed on the sidelines of a European leaders' summit because the political deadlock is an internal Spanish affair.

But he claimed his fellow leaders share his concern that Catalan authorities have acted against the rule of law and democracy.

A decision to force a January election is likely to further inflame tensions between Spain and Catalan pro-independence activists.

Catalonia's government said it has the mandate to declare independence from Spain after a referendum was held on October 1, and does not want a new election.

The central government will hold the special cabinet session tomorrow to begin the activation of Article 155 of Spain's 1978 Constitution, which allows for central authorities to take over all or some of the powers of any of the country's 17 autonomous regions.

The measure, which has never been used since democracy was restored after General Francisco Franco's dictatorship, needs to be approved by the Senate.

Rajoy's conservative Popular Party (PP) has an absolute majority in the Senate, so it should pass easily as early as October 27.

However, the PP has been holding talks with the main opposition Socialist party on the best way to apply Article 155 in the Catalan crisis, in order to gain a wider consensus.

Socialist party official Carmen Calvo said that an agreement had been reached with Spain's government on holding a new election in January in Catalonia.

Rajoy's government also reached agreement with the centre-right, pro-business Ciudadanos (Citizens) party.

The crisis over Catalonia's quest for independence escalated yesterday, as Spain's central government prepared to start activating Article 155 after Catalan president Carles Puigdemont refused to abandon the plans.

Puigdemont sent a letter to Rajoy just minutes before a deadline set by Madrid for him to backtrack on his calls to go independent.

Puigdemont did not give in, however, and threatened to go ahead with a unilateral proclamation of independence if the central government refuses to negotiate.

Spain's government responded by calling tomorrow's Cabinet session to activate Article 155.

Puigdemont and his aides have so far ruled out calling a snap vote as a way out of the deadlock.

In a sign that an explicit declaration of independence could be his response, as outlined in this week's letter, pro-independence MPs are holding talks about how to call a special regional parliament session as early as next week, according to far-left CUP party member Eulalia Reguant.