The Spanish government will block any attempt to further an independence process in Catalonia, spokesman Inigo Mendez de Vigo said, after the head of the northeastern region called a referendum on secession on October 1.
The region accounts for nearly one-fifth of Spain's economy, and has a population of 7.5 million.
"That referendum will not take place because it is illegal".
Last week, the Council of Europe's Venice Commission wrote to the Puigdemont government, urging him to carry out the referendum "in agreement with the Spanish authorities ... and in full compliance with the constitution and the applicable legislation", Catalan News Agency reported.
The Catalan government accused the Spanish government in Madrid of "abusing its powers to undermine" representatives in the region, while it is unclear how the impending legal battle over the legitimacy of the October poll will play out.
If Catalonia's pro-independence authorities win, they have said they will immediately start proceedings to separate from Spain.
The Spanish government, however, is confident that it can stop the referendum from happening in the first place.
The government of Catalonia says it has been open to negotiating the terms of the referendum or coming to an agreement, but has been ignored by Madrid.
Madrid may invoke Article 155 of the Spanish constitution, empowering the government to intervene in Catalonia's regional affairs, and may compel the autonomous administration to scrap the plebiscite.
Yahoo explained that the region did have a non-binding vote under then president Artur Mas, which yielded a vote of about 80% supporting independence, though only 2.3 million out of 6.3 million eligible voters took part.
Mas was later convicted of violating the court's order by holding the referendum and was barred from holding elective office for two years.
Around two million people in Catalonia voted in favor of secession at the time, although voter turnout was low.
Long coveting a split from Spain, the region's government also held an ultimately symbolic referendum in 2014, after it was challenged by the Spanish government in the Constitutional Court, who ruled it illegitimate.