The leader of Spain's Catalonia region, where a separatist movement is in full swing, on Friday announced an independence referendum for October 1 in defiance of Madrid.
People will be asked to vote on the question: "Do you want Catalonia to be an independent state in the form of a republic," Catalonia President Carles Puigdemont said in Barcelona.
If a majority votes "yes," the northeastern region's pro-independence government has said it will immediately start proceedings to separate from Spain.
A defiant Madrid immediately said that the Catalans' attempt to break away will be blocked.
"Any move that evolves from an announcement to a fact will be appealed by the government," Mendez de Vigo said. "That referendum will not take place because it is illegal."
"I don't want it, I don't believe in it, and as long as I am prime minister, it won't happen," Spain's Prime Minister Mariano Rajoy had said in May.
Spain's Constitutional Court has already ruled that independence referendum on Catalonia's future is illegal.
Referendum – an old demand
Catalonia, a wealthy, 7.5-million-strong region with its own language and customs, has long demanded separation from Spain.
For years, separatist politicians in the region have vainly tried to win approval from Spain's central government to hold a vote similar to Scotland's 2014 independence referendum from Britain, which resulted in a "no" vote.
While Catalans are divided on the issue, with 48.5 percent against independence and 44.3 percent in favour according to the latest regional government poll, close to three-quarters support holding a referendum.
In 2014, Catalonia held a non-binding vote under then-president Artur Mas, in which more than 80 percent of those who cast a ballot chose independence, although just 2.3 million out of 6.3 million eligible voters took part.
But in holding the symbolic referendum, Mas went against Spain's Constitutional Court, which had outlawed the vote – despite it being non-binding.
He was later put on trial and banned from holding office for two years.