"If the yes wins, if the no wins - in any scenario there must be mediation, because things aren't working", he said in an interview with the Agence France-Presse news agency.
"We must organize it so that there are long queues to give the image to the world that we are going to vote", instructions sent to voters read.
On the other hand, Carles Puigdemont promised that the referendum on the independence of Catalonia, a rich north-eastern province of 7.5 million people, would be held, although the Spanish court ruled that it was unconstitutional.
As the Spanish government continued trying to block an independence referendum scheduled to take place October 1 in Catalonia, on Saturday pro-independence voters occupied dozens of schools that had been designated as polling stations, in hopes of evading efforts by police officers to restrict access and stop the vote on Sunday.
"I think that from now it would be logical for the European Union to actively monitor (the situation) and actively take an interest", he said.
Opinion polls show Catalans are split on the issue of independence, but a large majority want to vote in a legitimate referendum to settle the matter.
The raid was meant to stop the use of vote-counting software linked to Sunday's referendum, Piqué said, adding that the Catalan government has an alternative to the software.
Catalan police already have sealed off 1,300 polling stations, or more than half of the 2,315 locations.
On Saturday, Spanish police also raided the Catalan government's telecommunications and information technology center, according to La Vanguardia citing RAC1 radio station.
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Their actions came a day after huge crowds massed in Barcelona, the regional capital, for a final campaign rally by independence supporters, many waving the distinctive Catalan flag.
The head of the Catalan regional police ordered officers to evacuate and close polling stations by 6 a.m. on Sunday, before the voting is due to open at 9 a.m.
Barcelona's Joan Brossa high school, for instance, advertised a series of activities including film screenings, football matches and Zumba dance fitness classes.
Millo said anyone remaining in schools after 6am will need to be removed in line with a judge's orders, but predicts there won't be significant problems.
The Catalan government is pressing ahead with a referendum in the face of obstruction by the Spanish executive, judiciary and the police.
The Catalan police, or Mossos d'Esquadra, who are monitoring the schools, are held in great affection by the Catalan people, especially after Islamist attacks in the region in August that killed 16.
Spain is divided into 17 autonomous regions, of which Catalonia is one.
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