There is evidence to support this.
In France this week, security agencies shut down three mosques. One was in Lagny-sur- Marne, a suburb of eastern Paris. Nine Muslims associated with that mosque were placed under house arrest and 22 others from barred from leaving France.
According to USA Today, in that investigation, police seized a 9mm handgun, a computer hard drive that was hidden behind a wall, as well as jihadist propaganda materials. Police also discovered documents about an unregistered Quranic school.
In addition, two other mosques, one in Gennevilliers in the northwest suburbs of Paris and one in Lyon, were closed by French police. Moreover, four Muslim "prayer rooms" in the Nice area in the south of France have also been shut down. It is worth noting that these so-called "prayer rooms" are very common throughout the West and are often operated in strip malls and in store fronts and private homes.
The Germans have been shutting down mosques for a few years now and, as of yet, they haven't been hit by a Paris or Brussels-style attack.
But they are good at keeping the door open to infect their neighbors.
Back in December, they shut down a mosque in Stuttgart that was involved in recruiting for the Islamic State: