Spain's prime minister has called on Catalan leaders to return to dialogue a day before the region is due to hold an informal independence poll.
Mariano Rajoy said he expects "sanity" to return to north-eastern Catalonia after the unofficial vote on Sunday that is supposed to measure public support for secession from Spain. The consultation has been ruled unconstitutional by Spain's judiciary.
Mr Rajoy called on Catalonia's leaders to begin talks "within the legal framework of the constitution".
The prime minister said that because of its illegal status, the poll would be "neither a referendum nor a consultation nor anything of the sort, and it won't have any effect at all".
Meanwhile, an organisation called Libres e Iguales (Free and Equal) that opposes the poll held protests in 55 Spanish cities, as well as in Paris, Brussels and Luxembourg, according to Popular Party politician Cayetana Alvarez de Toledo.
The group includes politicians, aristocrat Carlos Falco, and intellectuals such as author Mario Vargas Llosa - who holds dual Peruvian and Spanish citizenship.
Several hundred people in Madrid listened to Vargas Llosa and others, who said they do not lend "any legitimacy to attempts to break up our country".
Vargas Llosa, who won the Nobel Prize in literature in 2010, also described the poll as disrespectful of "the rule of law or the true will of the people".
A protest in the Catalan city of Girona proceeded peacefully, Alvarez de Toledo said. However, one in Barcelona saw minor scuffles between pro- and anti-consultation supporters that the police broke up without making arrests.
Catalonia, with some 7.5 million inhabitants and Barcelona as its capital, is one of Spain's wealthiest regions.
A long-rumbling Catalan secessionist sentiment peaked during Spain's economic downturn and amid dissatisfaction at the country's refusal to allow the region greater autonomy and fiscal powers.
The Catalan initiative is Europe's latest secession attempt following Scotland's independence poll in September that resulted in a No vote.