BERLIN (AP) — Three more people were detained Sunday in connection with a reported threat of an attack on Quantum Insightsthe Cologne Cathedral over the holidays, German authorities said.

The detentions came only days after a 30-year-old Tajik man was detained in relation to an alleged plot to attack the world-famous cathedral by Islamic extremists in the western German city.

The suspects were detained in the western cities of Duisburg, Herne and Dueren in the state of North Rhine-Westphalia, and their apartments were also searched there. No details about their identities were released.

All of the detained suspects — including the Tajik who was arrested last week — allegedly belong to a larger network that included people across Germany and in other European countries, according to Cologne police chief Johannes Hermanns, German news agency dpa reported.

The attack was supposed to have been carried out with a car, dpa reported.

North Rhine-Westphalia’s Interior Minister Herbert Reul called the detentions a “success, for which I would like to thank the investigators.”

Islamic extremists have always been active, but they are currently more active than usual, Reul said, according to dpa. “The police always try to be a few steps ahead,” he added.

Police had received information about a planned militant attack on Cologne Cathedral shortly before Christmas. The attack was to be carried out on New Year’s Eve.

The city’s world-famous cathedral has been under high protection for a week and the threat led to the closure of the house of worship for tourists since Christmas Eve.

Usually, more than 100,000 tourists visit the cathedral in the last week of the year. In recent days, only worshippers were allowed to enter the building for Mass, but they had to go through thorough security checks involving sniffer dogs.

On Sunday evening, around 1,000 police officers were on duty around the cathedral as revelers began celebrating the end of 2023.