Spain's constitutional court has suspended a Catalonian independence referendum while it considers a request from the central government to declare the vote unconstitutional.
The regional government of Catalonia had already said it will push ahead with preparations for the non-binding referendum on 9 November even if the court suspended the vote.
Spanish Prime Minister Mariano Rajoy earlier vowed to defend his country's "sovereignty" against an attempt by leaders in Catalonia to hold an independence vote
"There is nothing and no one, no power nor institution, that can break this principle of sole sovereignty," Mr Rajoy told reporters.
"Neither the object nor the proceedings of the vote are compatible with the Spanish constitution."
He made the comments as he announced that his government had filed a constitutional appeal against the planned vote.
While it could take years for the constitutional court to rule on the issue, the vote will be effectively suspended as soon as the court decides to accept the case.
The court said it would hold an emergency meeting today, with proceedings expected to start immediately.
Catalonia, which accounts for around a fifth of Spain's economy, has its own language and distinct culture and has long fought for greater autonomy.
Mr Rajoy said he regretted the decision by Catalonia's regional president to call the vote.
"I regret it because it's against the law, it's beyond democratic law, divides Catalans, distances them from Europe and the rest of Spain and seriously damages their welfare," Mr Rajoy said.
"Not to mention the frustration it causes to a large part of the Catalan people by encouraging them to participate in an initiative that, because it's illegal, won't see the light of day," he added.
Political analysts expect the Catalan leader to call early local elections after the vote is blocked, hoping for a victory to give his independence cause renewed momentum.
