Spain threatened on Wednesday to suspend Catalonia's autonomy if it follows through on its threat to break away as an independent country.
Prime Minister Mariano Rajoy has vowed to do everything in his power to prevent Catalan secession following a banned referendum in the region, which remains deeply divided over independence.
He held an emergency cabinet meeting after Catalonia's president Carles Puigdemont announced on Tuesday that he had accepted the mandate for "Catalonia to become an independent state."
Rajoy asked the Catalan leader to clarify whether he had actually declared independence, which could trigger moves by Madrid to suspend the region's semi-autonomous status.
The Catalan crisis is Spain's most serious political emergency since its return to democracy four decades ago.
World leaders are watching closely and uncertainty over the fate of the region of 7.5 million people has damaged business confidence.
Puigdemont said the referendum had given him a mandate for independence but immediately asked regional lawmakers to suspend the declaration to allow for negotiations with the central government.
Rajoy could choose to trigger constitution article 155, which allows Madrid to impose control over its devolved regions, a move many fear could lead to unrest.
The leader of the opposition Socialist Party, Pedro Sanchez, said meanwhile that his side and the government had agreed to study a possible constitutional reform" to try to end the crisis.
The debate would focus on "how Catalonia remains in Spain, and not how it leaves," Sanchez told reporters.
Unknown consequences
Following his declaration to parliament, Puigdemont and his allies signed an independence declaration outside the chamber, but its legal validity was unclear.
Regional government spokesman Jordi Turull said the declaration was "a symbolic act", adding that any official decision would need to be decided by the Catalan parliament.
Madrid has consistently said independence is not up for discussion.
"I did not expect independence to be declared today because of all the processes that the government of Spain has begun, both with police actions and with threats," Marc Cazes, a student in Barcelona, said on Tuesday.
Police violence against voters during the referendum vote sparked international concern.
The crisis has caused deep uncertainty for businesses in one of the wealthiest regions in the eurozone's fourth-largest economy.
Demands for independence in Catalonia, one of Spain's 17 semi-autonomous regions which has its own language and cultural traditions, date back centuries.
