The Basque parliament approved a measure on Thursday that says the Basque country has the right to secede from Spain, a move analysts described as the most serious threat to national unity since the establishment of democracy here nearly 30 years ago.
The measure, approved by a vote of 39 to 35, is part of a complex plan that calls for an overhaul of the region's relationship with the central government in Madrid.
"We express our will to form a new political pact," the plan says, "that grows from a new model for relations with the Spanish state based on freedom of association."
Before the vote, which was held in the Basque capital, Vitoria, Juan Jose Ibarretxe, the president of the Basque country and the main author of the plan, said, "We are not proposing a project for breaking away from Spain, but we are formalizing a project for friendly coexistence between the Basque country and Spain.
"The Basque country is not a subordinate part of the Spanish state," he added. "The only way there will be a shared relationship with the state is if we decide there will be one."
Political analysts said the vote gave momentum to the separatist movement in the Basque country, and presented the central government with the task of confronting the movement without inflaming it.
"This is the clearest push for independence that the Basque country has made," said Antonio Cano, a senior editor at the newspaper El Pais. "It is a very clear challenge to the unity of Spain. I'd say it places the country in its biggest crisis of unity since democracy began here."
For nearly 40 years, the various regions that make up Spain were kept together by the iron fist of dictator General Francisco Franco. But since his death in 1975, some analysts have wondered if a democratic government would be able to keep the country united. The central government has said that it is willing to discuss requests for greater autonomy, but has rejected the claim that the Basque region has the right to unilaterally determine its relationship with Madrid.
"We've made it very clear," Spanish Deputy Prime Minister Maria Teresa Fernandez de la Vega said. "The plan goes against the Constitution."
The plan now moves to the national parliament, where it will surely be rejected, analysts said. But supporters of the plan said defeat would not stop them from submitting it to a popular referendum.
Thursday's vote has surprised analysts, who expected the measure to fail to gain the support of a small group of separatists who had said the plan was too moderate. But three members of the group, a party known as Sozialista Abertzaleak, decided to support it, providing enough votes for the majority needed for passage.