The dispute has plunged Spain into one of its biggest political crises since the restoration of democracy in the 1970s after decades of military dictatorship. Prime Minister Mariano Rajoy has said the referendum is against the law and the constitutional court has ordered it be halted while its legality is determined.
Catalonia's separatist government, however, remains committed to holding it on Sunday.
Catalonian independence vote would not hurt Spain's rating
Rajoy, speaking on Tuesday alongside US President Donald Trump in Washington, said it would be "ridiculous" if the affluent northeastern region declared independence from Spain.
Trump said he opposed the referendum and wanted a united Spain. "I really think the people of Catalonia would stay with Spain. I think it would be foolish not to," he told reporters.
Senior Spanish government officials said on Tuesday authorities had done enough to prevent a meaningful referendum as Catalonia lacked an election commission, ballot boxes, ballot papers, a transparent census and election material.
"Today we can affirm that there will be no effective referendum in Catalonia. All the referendum's logistics have been dismantled," the Spanish government's representative in Catalonia, Enric Millo, told reporters in Barcelona.
Catalonia sets vote on independence from Spain for October 1
Catalonia's prosecutor has ordered the regional police - known as the Mossos d'Esquadra - to take control of any voting booths by Saturday, a spokesperson for the Madrid government's Catalan delegation said.
In an order to police issued on Monday, the prosecutor's office said they would take the names of anyone participating in the vote and confiscate relevant documents. Anyone in possession of the keys or entrance codes to a polling booth could be considered a collaborator to crimes of disobedience, malfeasance and misappropriation of funds, the order said.
Unrelenting opposition
The Madrid government has in recent weeks taken political and legal measures to prevent the referendum by exerting more control over the use of public funds in Catalonia and arresting regional officials.
Hundreds of police reinforcements have been brought into Barcelona and other cities. Madrid has also threatened fines against bureaucrats working on the ballot, including the region's election commission, which was dissolved last week.
Huge crowd to rally for Catalan independence before vote
These actions have provoked mass demonstrations and drawn accusations from Catalan leaders that the Madrid government was resorting to the repression of the Franco dictatorship. A "yes" vote is likely, given that most of the 40 percent of Catalans who polls show support independence are expected to cast ballots while most of those against it are not.
But the unrelenting opposition from Madrid means such a result would go all but unrecognised, potentially setting up a new phase of the dispute.
The Catalan regional government, which plans to declare independence within 48 hours of a "yes" victory, maintained on Tuesday the vote will go ahead and it sent out notifications to Catalans to man polling booths across the region.
Many had not yet received information about where or when they would be working after the state-run postal service was ordered to stop all mail related to the vote, a parliamentary spokesperson for one separatist party said.
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