Cataluña's disputed president Carles Puigdemont could be jailed for 30 years
The Spanish Foreign Minister Alfonso Dastis has said "reality is already sinking in" for Catalonia after Madrid dismissed the parliament.
He said authorities intend to restore law and order in the autonomous region after the regional parliament declared itself independent of Spain.
He said: "It was difficult indeed but let me tell you that those who disregarded autonomy were the former Catalan government and those who supported them because they simply stopped convening the parliament, they simply stopped going.
"What we intend to do is to restore the Catalan law, first and foremost, in Catalonia and to give a say to the Catalan people in order to make sure both the Catalan law and the Spanish constitution are respected.
"We are not taking autonomy away from Catalonia. We are just re-establishing it in fact."
Hundreds of thousands of anti-independence protesters, chanting "Viva España" (long live Spain) and "Prison for Puigdemont", marched through the centre of Barcelona carrying Spanish and Catalan flags on Sunday.
Police estimated the turnout was 300,000, while organisers said more than one million joined the rally.
A poll - the first to be published since the regional election was called - gave political parties opposing independence for Catalonia a small lead.
The government in Madrid sacked Catalan regional president Carles Puigdemont and dismissed the parliament on Friday.
Mr Puigdemont, who is facing arrest on charges of "rebellion", called on Saturday for Catalan people to peacefully oppose Madrid's takeover of the region.
He has said he does not accept his dismissal, with the Catalan government saying it was given a mandate to secede from Spain following the referendum on October 1st.
Asked whether Mr Puigdemont could continue in office, Mr Dastis said: "We don't think he will have the means to run a parallel government.
"We hope that the administration, the civil servants in Catalonia, will respect the measures that have been taken and that they will go on implementing those ordered and go on ensuring that the public services are delivered in Catalonia.
"Reality is already sinking in, will continue sinking in and they will realise that they cannot do something without the authority of law and they will be usurping authority.
"We are there to ensure, that for a limited time, that normality is restored in Catalonia, that life can go on and that elections can be organised in order for the Catalan people to decide their own future."
He added that Mr Puigdemont could be eligible to stand in regional elections on December 2121, which were called after Madrid dissolved the Catalan parliament - provided "he is not put in jail at that time".
Secessionists won 48% of the vote in Catalonia in the last regional election in 2015, but won more seats because Spanish election law gives more weight to sparsely-populated area.
On Saturday, the Department of Foreign Affairs re-affirmed that Ireland does "not accept or recognise" the declaration of independence.