Pope Leo XIV will give an unprecedented address on Monday to the Spanish parliament and is set to meet with victims of sexual abuse by clergy.
The closed-door meeting, reported by Spanish media, is already clouded in controversy, as some of the main victims' associations said they were not invited.
Juan Cuatrecasas, spokesman for the association Infancia Robada (Stolen Childhood), told AFP it was a "blow".
He said the pope risked seeing "a completely skewed reality" if he met only with victims assisted by the Repara project of the archdiocese of Madrid.
Spanish media said the meeting would take place on Monday afternoon at the Vatican embassy in the Spanish capital, formally known as the apostolic nunciature.
The Vatican earlier said in a statement the pope would speak to victims during his seven-day visit to Spain.
But it did not say when or where, adding that it would not give further information until after the meeting out of "respect for the victims".
Speaking to reporters on the flight to Madrid on Saturday, the 70-year-old leader of the world's 1.4 billion Catholics said the scandal of abuse was "still an open wound" for the Church.
Around 200,000 minors are estimated to have suffered abuse by clergy in Spain since 1940, according to a 2023 report from Spain's national ombudsman.
Prime Minister Pedro Sanchez's government and the Catholic Church in Spain signed an agreement in March to compensate victims, after years of reticence and opacity from the Church hierarchy.
After welcoming the pope on Saturday, Spanish King Felipe VI hailed his "clarity and firmness" on the issue, saying they were "essential in the process of healing and reparation of the damage inflicted".
The US-born pope will give a speech to the Spanish parliament earlier on Monday.
Popes rarely address parliaments, trying to avoid overt political interventions.
On Saturday, Leo had called in a speech at Spain's royal palace for an end to "divisive and polarising rhetoric", an appeal that resonates in a country where political life is highly polarised and has, in recent years, been marked by the emergence of far-right party Vox, now the nation's third-largest political force.
The pope's visit to Spain comes at a particularly sensitive and turbulent time for Sanchez, who is under attack from critics over several corruption scandals involving his inner circle.
Before the speech, expected at 0830 GMT, Leo will meet with Sanchez.
During his visit, the pope has praised Spain's "active commitment to peace" and "faithful adherence to international law".
Spain's left-wing government has repeatedly clashed with US President Donald Trump over Iran, and with Israel over the war in Gaza.
The pontiff himself has been harshly criticised by Trump for his anti-war views, particularly since the United States and Israel began the war on Iran on February 28.
A day after celebrating an open-air mass that organisers said was attended by more than 1.5 million people in Madrid, the pope will also hold another large gathering at football club Real Madrid's famed Bernabeu Stadium on Monday.
He will then travel to Barcelona, where on Wednesday he will bless the new tower of the Sagrada Familia Basilica -- a still-unfinished masterpiece by revered architect Antoni Gaudi that recently became the world's tallest church.
In the Canary Islands on Thursday and Friday, Leo will be joined by Sanchez to honour thousands of migrants who have died trying to reach Europe.
In contrast with many of its European allies, Spain under Sanchez's left-wing government has a relatively liberal immigration policy.
But the government is under pressure on the issue from the main conservative Popular Party and from Vox.
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