Catalan leader Carles Puigdemont came under pressure from one of his key allies on Friday to declare full independence and ignore a threat of direct rule from the Spanish government.

Puigdemont made a symbolic declaration of independence on Tuesday night, only to suspend it seconds later and call for negotiations with Madrid.

Spain's Prime Minister Mariano Rajoy has given him until Monday to clarify his position - and then until Thursday to change his mind if he insists on a split - threatening to suspend Catalonia's autonomy if he chooses independence. But far-left Catalan political group CUP called on Puigdemont to make an unequivocal declaration of independence in defiance of the deadlines.

"If [the central Madrid government] wants to continue to threaten and gag us, they should do it to the Republic that has already been claimed," the party said.

It was the first time that Spanish Prime Minister Mariano Rajoy openly said that Article 155 of the Spanish constitution will be the next step taken by the government if Catalan authorities don't backtrack. He said the government "wants to offer certainty to citizens" and that it is "necessary to return tranquility and calm." Under that article, the central government could take control of the governance of a region, a never-before used provision that has been referred to as the "nuclear option."

Article 155 of the Constitution allows the central government to take some or total control of any of its 17 regions if they don't comply with their legal obligations. This would begin with a Cabinet meeting and a warning to the regional government to fall into line. Then, the Senate could be called to approve the measure.

The CUP only holds 10 seats in the 135-seat Catalan parliament. But Puigdemont's minority government relies on its support to push through legislation and cannot win a majority vote in the regional parliament without its backing.

The wealthy region's intention to break away after a referendum has plunged Spain into its worst political crisis since an attempted military coup in 1981.

Sources close to the Catalan government said Puigdemont and his team were working on an answer to Rajoy though they declined to say what line he might take.

The CUP statement echoes the position expressed late on Thursday by influential pro-independence civic group Asamblea Nacional Catalana which said: "Given the negative position of Spain toward dialogue, we ask the regional parliament to raise the suspension [on the declaration of independence]."

But the leader of Puigdemont's party, Artur Mas, who served as the region's president until 2016 and is still believed to influence key decisions, said on Friday declaring independence was not the only way forward.

"If a state proclaims itself independent and cannot act as such, it's an independence that is merely aesthetic," he told Catalan television TV3. "The external factor must be taken into account in the decisions that will be made from now on," he said.

The European Union, the United States and most other world powers have made it clear they wanted Catalonia to remain within Spain.

"If we allow Catalonia - and it is none of our business - to separate, others will do the same. I do not want that," Jean Claude Juncker said in a speech at Luxembourg University.