The capital of Islamic radicalism in Switzerland has been struck a blow after authorities arrested a prominent imam for inciting violence toward moderate Muslims.

The Swiss city of Winterthur has become the capital of Islamic extremism in recent years largely due to the radical An’Nur mosque. This week a prominent imam was arrested on charges that he advocated for his followers to murder moderate Muslims, reports Swiss paper Blick.

According to police an imam of Ethiopian origin delivered a sermon on October 21st which called for his followers to denounce and murder Muslims who refuse to participate in common prayers. A further three other members of the mosque were also arrested by authorities and their homes searched.

Among those arrested was Atef Sahnoun, president of the club that facilitates the mosque. Witnesses claim that police arrived at Sahnoun’s house in the early hours of the morning to arrest him with at least four police vans.

Four more people detained were found to be illegal migrants from Algeria, Tunisia, and another unnamed country. The migrants had slept at the radical mosque and are said to be from 23 to 35 years old. Police did not comment on whether any of the men may have ties to Islamist groups or Islamic State.

Police focussed on Sheik Abdul Rahman, a recent immigrant from Somalia, who is said to be the head preacher after the departure of former imam Sheik Wail who was linked to radical Islamic rhetoric. The police would not confirm whether the imam in custody was Rahman.

The An’Nur Mosque has become the heart of Islamic radicalism in Switzerland with police uncovering a jihadi sleeper cell linked to the mosque late last year. Prominent Swiss journalist Kurt Pelda said: “We do not know exactly what he has done in Syria but there is every indication it has to do with ISIS… ISIS has a cell in Winterhur in the An’Nur mosque, let there be no doubt.”

As a result of the revelation, local authorities opened a de-radicalisation centre in the city. The continued presence of the mosque and the radical preachers who speak there may harm any attempts to keep young Muslims, who are becoming increasingly radicalised throughout Europe.