The southern Austrian city of Graz is now being labelled a “stronghold” of radical extremism after a new report revealed that half of the mosques in the city are suspected of preaching radical Islam.

Experts say that 11 out of the 20 mosques in the city have links to radical Islamic theology and are under constant surveillance by domestic intelligence and police.

Authorities have also proven that many of those radicalised in mosques in the city have travelled to the Middle East to fight for the Islamic State terror group, with around a dozen having recently returned, Kronen Zeitung reports.

Several large-scale raids have also occurred on mosques in the city, forcing some of them to shut down because of alleged links to terrorist groups.

In 2014, the Furkan Mosque and the Tawhid Mosque were both accused of recruiting for the Islamic State. Later in the year 40 residences and prayer houses were raided by police, leading to the arrest and imprisonment of several jihadists.

An imam from Graz who worked in the Austrian prison system has most recently been linked to a plot to stage a revolt to free incarcerated extremists. The cleric, an Egyptian migrant who was formerly a taxi driver, was originally hired to help deradicalise extremist prisoners.

Radical Islamist ‘Hate Books’ Found in Austrian Prison Library

https://t.co/yg6rcRyLP0 — Breitbart London (@BreitbartLondon) October 23, 2017

Earlier this year Islamic extremist Salafist literature was found in an Austrian prison, leading to Justice Minister Wolfgang Brandstetter admitting that authorities had found at least 30 radical Islamic books in various Austrian prisons. The incident stoked fears that Islamic radicalisation may be occurring within the Austrian prison system.

Last week a 25-year-old Bosnian migrant was arrested in Graz after police caught him plotting to attack the city’s Christmas market. The man, who lived at a local homeless shelter, constantly looked at terror-attack videos on the shelter’s shared computer, and even asked workers how he could rent a vehicle in order to emulate last year’s Berlin attack.