Prime Minister Pedro Sánchez said the release was "the best decision for Catalonia and the best decision for Spain."
The biggest threats to rule of law, peacekeeping and individual freedoms in Spain and Europe stem from violent expressions of exclusionary nationalism and populism.
Nine Catalan leaders were sentenced to between nine and 13 years in prison by the Spanish supreme court on Monday.
Spanish police have shut down polling places to stop voters from voting on an independence referendum.
Spain is far from descending into full-scale conflict. But the Catalan independence debate has the potential to prove seriously destabilizing.
The Spanish government has declined to rule out any options for preventing the vote from taking place.
A series of trials of Catalan politicians should shock the democratic soul of any European.
Spain's central government is largely paralyzed after two inconclusive elections while Catalonia pushes toward 2017 independence plan.
'There's no alternative to Catalan independence. You'd have to be very radical to defend what we have now,' Puigdemont says.
The move comes as Spain faces weeks of uncertainty following an inconclusive general election.
Four parties will likely elect the same number of MPs in the region.
The court's decision deepened a stand-off over the potential breakaway.
UEFA have fined Barcelona for fans flying the flags twice this year.
Pro-independence parties received 47.9 percent of the total vote.
Spain is to sue Catalan president Artur Mas after he defied a court injunction not to hold a vote on secession, potentially barring him from running in regional elections
Hackers have targeted pro-independence campaign sites and local Catalan government web pages, while crank calls have kept organiser's line busy
"We have earned the right to a referendum," said Catalan leader Artur Mas, after two million people voted for independence from Spain
The Spanish state adviser backed a veto of a watered-down Catalan vote, making it likely the government will try and have the planned "consultation of citizens" blocked by the courts
Catalonia is set to push ahead with a referendum on independence, despite Madrid's moves to block the vote
Catalonian leader Arthur Mas signed a decree on Saturday calling for a vote on November 9, putting the local government on a collision course with Madrid
Inigo Mendez de Vigo said that Scotland would almost certainly have to adopt the euro, and would have to wait at least five years to join the EU
Emboldened by the Scottish independence campaign Catalan protesters plan rally in support of break from Spain