In recent years, attendance at La Diada events, as the National Day is known, has fallen as support for breaking away from Spain has decreased.

But the two Catalan parties are now in the middle of negotiations to form a new government and are hoping the talks may boost the flagging independence cause ahead of regional elections in 2025.

Acting Prime Minister Pedro Sanchez would need the seven lawmakers of the hardline conservative Junts per Catalunya party and the seven votes from the more moderate Esquerra Republicana de Catalunya (ERC) to form a government following an inconclusive general election in July.

After exiled Junts leader Carles Puigdemont last week insisted on an amnesty for pro-independence leaders as a condition for talks, his rival at the ERC, Pere Aragones, on Sunday went a step further, raising the spectre of a referendum.

"An amnesty alone will not resolve the sovereignty conflict with the state. Catalonia wants a free vote on independence," Aragones, who is president of the region, said on Sunday in Barcelona.

Puigdemont, living in Belgium as a fugitive from Spanish justice for attempting secession five years ago, laid out tough conditions for his party's support in parliament for Sanchez to stay in power.

"Whatever political agreement we reach, whatever we propose, will be to move closer to the goal of every nation, which is to be a free and independent state," Junts General Secretary Jordi Turull said at an event connected to La Diada on Monday.

This past week Puigdemont called for Spain to abandon judicial actions against separatists, though he stopped short of demanding a new vote on independence.

"Catalonia has opened up a new path of progress, understanding and coexistence. It is time to look to the future and move forward," Sanchez wrote on Monday on X, formerly known as Twitter .

Aragones's comments on Sunday suggest that the ruling left-wing coalition led by Sanchez cannot necessarily bank on ERC's support.

With ERC competing against Junts in elections for Catalonia's regional parliament due in early 2025, Aragones appears to be hardening his stance and upping the rhetoric.

Isabel Rodriguez, the acting government spokesperson, said Spain would not do anything which contravenes the constitution.

Alberto Nunez Feijoo, whose conservative People's Party (PP) won the most votes on July 23, will take the first stab at a vote to form a government on Sept. 27, but his chances are seen as slim since his party opposes any concessions to separatists.

In July, a survey published by the Catalan Centre for Public Opinion (CEO), operated by the regional government, found 52% opposed splitting from Spain while 42% supported independence.

(Reporting by Graham Keeley and Inti Landauro; Writing by Charlie Devereux; Editing by Peter Graff and Sharon Singleton)