The police said in a statement that they would use tracker dogs to check the cathedral after evening mass and then close it off. On Sunday, Christmas Eve, they would carry out a security check on all visitors and recommended that they get to services early.

Police said they could not elaborate, citing the ongoing investigation.

German newspaper Bild earlier reported that security authorities in Austria, Germany, and Spain had received indications that an Islamist group intends to carry out attacks during the Christmas and New Year festivities.

In recent weeks, interior minister Nancy Faeser has warned of the rising threat of Islamist violence in Germany and elsewhere in Europe as the Israel-Hamas war increases the risk of radicalisation.

Austrian police said in a statement they were increasing security in churches and Christmas markets given a heightened state of alert.

“Given that terrorist actors throughout Europe are calling for attacks on Christian events, especially around Dec 24, the security authorities have taken the corresponding protection measures in public spaces,” the police said.

Spain’s interior ministry announced at the beginning of December a reinforcement of security measures from Dec 18 for the Christmas holidays, with the anti-terrorism alert at level 4 or “high risk,” as it has been since June 2015.