MADRID (Reuters) - Tens of thousands of people waving Spain’s red-and-yellow flag demonstrated in Madrid on Sunday to oppose any concessions by the government to Catalan pro-independence parties and to call for early elections.

Demonstrators chanting “Spain! Spain!” and “We want to vote!” filled the Plaza de Colon in the city center in the largest protest Socialist Prime Minister Pedro Sanchez has faced in eight months in office.

The opposition center-right and far-right parties called the rally, seeking to make a show of force against Sanchez by capitalizing on anger with Catalonia’s separatist leaders and the government’s efforts to establish a dialogue with them.

Around 45,000 people attended, officials said.

The government’s proposal last Tuesday to appoint a rapporteur in talks among political parties to address the Catalan independence crisis galvanized the opposition, which has deemed it a betrayal and a surrender to pressure from Catalan separatists.

“The time of Sanchez’s government has ended,” Popular Party leader Pablo Casado told reporters before the protest. Some banners at the rally read “Sanchez, liar” and “Spain is not negotiable and cannot be sold”.

Sanchez, who replaced a conservative government last June in a vote of confidence, holds just a quarter of the seats in parliament and relies on backing from anti-austerity party Podemos, Catalan nationalists and other small parties to pass laws.

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The government is squeezed on both sides of the Catalan issue: Deputy Prime Minister Carmen Calvo said on Friday the talks were on track to fail because Catalan pro-independence groups had rejected the government’s proposed framework. The Catalan groups want a referendum on independence included on the agenda, which Madrid will not accept.

UNITY?

Ana Puente, a 73 year-old retiree who attended the gathering, said she was protesting for a “united Spain”.

“The government is giving many things to supporters of Catalan independence and is going to break Spain apart,” said Raquel García, 76, who was carrying a Spanish flag.

Sanchez rejected that argument, telling a separate rally in the northern city of Santander: “The government works for the unity of Spain and that means to unify Spaniards and not to put one against the other as the right is doing today in Colon square.”

The protest took place two days before the start of the trial of 12 Catalan independence leaders, who face up to 25 years in prison on charges of rebellion and misuse of public funds for their role in a failed secession bid from Spain that they are accused of spearheading in 2017.

The government faces a key vote on Wednesday on its 2019 budget proposal, which will likely fail without the support of Catalan parties. But those parties have said their vote for the budget is conditional on the Catalan talks including the issue of independence, something the government will not include.

Failure by parliament to approve the budget bill could prompt a snap election before the next scheduled vote in 2020.

Recent opinion polls have shown the conservative Popular Party, center-right Ciudadanos and far-right Vox could together win a majority of seats in parliament if elections were held, allowing them to replace the Socialist government.