Catalonia's High Court asked for Spanish national police to provide extra security at the court building in the event of the Catalan parliament declaring independence; the building is currently guarded by local police
The leader of Spain's Socialist opposition party, Pedro Sanchez, told reporters in Barcelona that his party would back government action if independence was declared unilaterally on Tuesday: "We reach out for dialogue but we'll support the response of the rule of law in the face of any attempt to break social harmony"
A 'great democracy'
"If there was a declaration of independence, it would not be recognised," Ms Loiseau told French broadcaster CNews (video in French).
"The first consequence would be its exit from the European Union."
"Obviously," she added, "there is more to Catalonia than the consultation organised by the independence movement...
"This crisis needs to be resolved through dialogue at all levels of Spanish politics."
Casting doubt on the validity of the vote, she described Spain as a "great democracy" and pointed to the "particularly" high level of devolution its regions already enjoyed.
However, Catalans have long been calling for more say in spending, higher status for their language and recognition that they are a nation distinct from Spain.
All eyes on Puigdemont
Catalonia's parliament had been due to meet on Monday with the expectation that it would endorse the declaration of independence, based on the majority Yes vote on 1 October.
However, the session was blocked by the Spanish Constitutional Court, which had likewise sought to stop the referendum itself.
Speculation is intense as to what Mr Puigdemont may say when he addresses the parliament in Barcelona on Tuesday evening.
He could ask the parliament to declare independence on the basis of the referendum law it passed last month, which in turn could lead the Spanish government of Prime Minister Mariano Rajoy to suspend devolution, acting under Article 155 of the constitution.
The BBC understands that whatever Mr Puigdemont says, his statement will trigger the 48-hour period within which MPs need to declare independence, according to the Catalan law.