MADRID (AP) — Spain’s Socialist Party has struck a deal with a fringe Catalan separatist party to grant an amnesty for potentially thousands of people involved in the region’s failed secession bid in exchange for its key backing of acting Spanish Prime Minister Pedro Sánchez in forming a new government.

Socialist lawmaker and party official Santos Cerdán announced the deal on Thursday in Brussels after sealing the agreement with the party led by Carles Puigdemont, who fled to Belgium after leading the failed 2017 independence attempt for Catalonia.

“This a political agreement and an agreement for an amnesty,” Cedrán said.

The decision greatly boosts Sánchez’s chances of forming another minority leftist coalition government. Sánchez, a Socialist and Spain’s leader since 2018, still needs the backing a small Basque party but he is likely to achieve that.

An amnesty has been the crucial part of difficult negotiations by representatives of Sánchez’s caretaker leftist government to win the support of two Catalan pro-independence parties. The backing of Puigdemont’s Junts (Together) and their rival Republican Left of Catalonia party, which gave its backing to Sánchez last week, is vital if Sánchez is to be reelected prime minister following an inconclusive national election in July.

While the two radical parties hold just seven seats each in the 350-member parliament, only they can put Sánchez over the necessary threshold of 176 votes in an investiture session that is expected to be held in the coming days. If no government can be formed by Nov. 27, the parliament would be dissolved and new elections called for January.

The amnesty would benefit Puigdemont and scores of people, from minor government officials to ordinary citizens, who ran into legal trouble for their roles in Catalonia’s illegal secession attempt that brought Spain to the brink of rupture six years ago.

Spain’s courts are still trying to have Puigdemont extradited from Belgium, where he fled in 2017 to avoid arrest. Given that he is considered an enemy of the state for many Spaniards, any deal that benefits him is politically toxic.

Cedrán said the amnesty legislation, which will need the support of several smaller left-wing and regionalist parties to be passed, will cover all crimes and alleged crimes related to the Catalan separatist movement from 2012 until now.

“Six years have passed (since the secession attempt) and the conflict is still unresolved,” Cedrán said. “Our goal is to start a new chapter … where the errors of the past are no longer obstacles to overcome.”

The amnesty is fiercely opposed by the main conservative opposition Popular Party and the far-right party Vox as well as by many in the judiciary.

Tens of thousands of people have rallied in Madrid and Barcelona against the amnesty in recent weeks.

Protests backed by Vox turned nasty on Monday and Tuesday night with police having to use batons and tear gas to protect the headquarters of Sánchez’s Socialist party in Madrid. More protests have been called by the Popular Party for Sunday.

The amnesty talks have also fallen under the scrutiny of the European Union. EU Commissioner of Justice Didier Reynders sent Spain’s government a request for more information this week.

It is likely to end up in Spain’s Constitutional Court for a judicial review.

Even though support for Catalan separatism lost support in the July election, Junts and Republican Left for Catalonia used their leverage given to them by the fragmented chamber and made an amnesty law a prerequisite for supporting Sánchez. They also demanded an independence referendum in the region, but Sánchez has so far ruled that out.

Prior to the election outcome, Sánchez was opposed to an amnesty. But now he says an amnesty is necessary to bring about a return to normal political life in the northeast region.

When Sánchez came to power, he inherited a Catalonia with around half the population wanting independence and where there were regular protests in Barcelona and other towns that sometimes turned violent. His decision to grant pardons to several leaders of the movement helped to reduce tensions and chipped into the popular support for separatist parties.

No one doubts that he is now willing to sweep away their alleged crimes purely out of political necessity, given how divisive the Catalan independence issue is both inside Catalonia and the rest of Spain. Even former Socialist Prime Minister Felipe González has said that Sánchez wouldn’t be doing it if he didn’t need the extra parliamentary support.

Puigdemont considers himself a political exile, while Spain’s government and many Spaniards say he is a politician who violated the law when he defied court warnings and held an authorized independence referendum in October 2017 before issuing a declaration of independence that won no international recognition. He then slipped across the border to avoid a legal crackdown that landed several of his Cabinet members in prison.

While admitting that his Socialists and the separatists are still diametrically opposed on their vision of a united, or divided, country, Cedrán said that the deal is not just to help Sánchez form a government, but to secure the separatists’ support during the entire four-year legislature.

Given Puigdemont’s track record of trying to destabilize the Spanish state, many expect the legislature to be a bumpy ride for Sánchez.

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Wilson reported from Barcelona, Spain.